Quarterly report pursuant to Section 13 or 15(d)

DEBT FINANCING - Narrative (Details)

v2.4.1.9
DEBT FINANCING - Narrative (Details) (USD $)
 0 Months Ended 1 Months Ended 3 Months Ended 2 Months Ended 0 Months Ended 1 Months Ended
Jan. 01, 2015
property
Jan. 31, 2015
property
Mar. 31, 2015
property
Mar. 31, 2014
May 31, 2015
property
Apr. 01, 2014
financial_institution
component
Jun. 03, 2015
Jun. 05, 2015
Dec. 31, 2014
Debt Instrument [Line Items]                  
Debt financing     $ 618,290,000us-gaap_DebtLongtermAndShorttermCombinedAmount           $ 597,691,000us-gaap_DebtLongtermAndShorttermCombinedAmount
Number of self storage properties acquired 5us-gaap_NumberOfBusinessesAcquired 6us-gaap_NumberOfBusinessesAcquired 6us-gaap_NumberOfBusinessesAcquired            
Liabilities assumed, mortgages     16,442,000nsa_BusinessCombinationConsiderationTransferredLiabilitiesIncurredMortgages            
Repayment of long term debt     16,489,000us-gaap_RepaymentsOfLongTermDebt 501,000us-gaap_RepaymentsOfLongTermDebt          
Subsequent Event [Member]                  
Debt Instrument [Line Items]                  
Number of self storage properties acquired         21us-gaap_NumberOfBusinessesAcquired
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		       
Related Party Note [Member]                  
Debt Instrument [Line Items]                  
Debt financing     4,054,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_RelatedPartyNoteMember 		          0us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_RelatedPartyNoteMember
Effective interest rate     3.30%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= nsa_RelatedPartyNoteMember 		           
Line of Credit [Member] | Credit Facility [Member]                  
Debt Instrument [Line Items]                  
Maximum borrowing capacity           425,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		     
Number of financial institutions in lender agreement           7nsa_LineOfCreditFacilityNumberOfLenders
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		     
Number of lender agreement components           2nsa_LineOfCreditFacilityNumberOfComponents
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		     
Line of Credit [Member] | Credit Facility [Member] | Revolving line of credit [Member]                  
Debt Instrument [Line Items]                  
Maximum borrowing capacity     198,700,000.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		    280,400,000.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		     
Debt financing     182,217,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		          166,217,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
Effective interest rate     2.78%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		           
Borrowing base calculation, minimum occupancy rate of property           75.00%nsa_LineOfCreditFacilityBorrowingBaseCalculationMinimumOccupancyRateofProperty
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		     
Extension fee, percent     0.20%nsa_LineOfCreditFacilityExtensionFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		           
Line of Credit [Member] | Credit Facility [Member] | Revolving line of credit [Member] | London Interbank Offered Rate (LIBOR) [Member]                  
Debt Instrument [Line Items]                  
Reduced borrowing rate     2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember 		           
Line of Credit [Member] | Credit Facility [Member] | Revolving line of credit [Member] | Minimum [Member]                  
Debt Instrument [Line Items]                  
Unused borrowing capacity, percent           0.20%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember 		     
Line of Credit [Member] | Credit Facility [Member] | Revolving line of credit [Member] | Maximum [Member]                  
Debt Instrument [Line Items]                  
Unused borrowing capacity, percent           0.30%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		     
Line of Credit [Member] | Credit Facility [Member] | Revolving line of credit [Member] | Subsequent Event [Member]                  
Debt Instrument [Line Items]                  
Repayment of line of credit             96,300,000us-gaap_RepaymentsOfLinesOfCredit
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		   
Line of Credit [Member] | Credit Facility [Member] | Revolving line of credit [Member] | Subsequent Event [Member] | London Interbank Offered Rate (LIBOR) [Member]                  
Debt Instrument [Line Items]                  
Reduced borrowing rate               1.60%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember 		 
Line of Credit [Member] | Credit Facility [Member] | Term Loan [Member]                  
Debt Instrument [Line Items]                  
Maximum borrowing capacity           144,600,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= nsa_TermLoanMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		     
Debt financing     144,558,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_CreditFacilityAxis
= nsa_TermLoanMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		          144,558,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_CreditFacilityAxis
= nsa_TermLoanMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
Effective interest rate     3.65%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_CreditFacilityAxis
= nsa_TermLoanMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember 		           
Line of Credit [Member] | Credit Facility [Member] | Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]                  
Debt Instrument [Line Items]                  
Reduced borrowing rate     2.40%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= nsa_TermLoanMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember 		           
Line of Credit [Member] | Credit Facility [Member] | Term Loan [Member] | Subsequent Event [Member] | London Interbank Offered Rate (LIBOR) [Member]                  
Debt Instrument [Line Items]                  
Reduced borrowing rate               1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= nsa_TermLoanMember
/ us-gaap_DebtInstrumentAxis
= nsa_CreditFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember 		 
Loans Payable [Member] | Unsecured Term Loan [Member]                  
Debt Instrument [Line Items]                  
Debt financing     50,000,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember 		          50,000,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember
Effective interest rate     5.18%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember 		           
Debt Instrument, Face Amount     50,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember 		    50,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember 		     
Debt Instrument, Number Of Lenders           3nsa_DebtInstrumentNumberOfLenders
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember 		     
Maturity date extension fee     250,000nsa_DebtInstrumentMaturityDateExtensionFee
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember 		           
Loans Payable [Member] | Unsecured Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]                  
Debt Instrument [Line Items]                  
Reduced borrowing rate     5.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember 		    5.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember 		     
Loans Payable [Member] | Unsecured Term Loan [Member] | Base Rate [Member]                  
Debt Instrument [Line Items]                  
Reduced borrowing rate           4.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= nsa_UnsecuredTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember
/ us-gaap_VariableRateAxis
= us-gaap_BaseRateMember 		     
Mortgages [Member] | Fixed Rate Mortgages [Member]                  
Debt Instrument [Line Items]                  
Debt financing     153,961,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_FixedRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		          153,416,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_FixedRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
Effective interest rate     4.07%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= nsa_FixedRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		           
Minimum effective interest rate     2.20%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMinimum
/ us-gaap_DebtInstrumentAxis
= nsa_FixedRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		           
Maximum effective interest rate     5.15%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMaximum
/ us-gaap_DebtInstrumentAxis
= nsa_FixedRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		           
Mortgages [Member] | Fixed Rate Mortgages [Member] | Subsequent Event [Member]                  
Debt Instrument [Line Items]                  
Number of self storage properties acquired             11us-gaap_NumberOfBusinessesAcquired
/ us-gaap_DebtInstrumentAxis
= nsa_FixedRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		   
Liabilities assumed, mortgages             28,600,000nsa_BusinessCombinationConsiderationTransferredLiabilitiesIncurredMortgages
/ us-gaap_DebtInstrumentAxis
= nsa_FixedRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember 		   
Mortgages [Member] | Variable Rate Mortgages [Member]                  
Debt Instrument [Line Items]                  
Debt financing     83,500,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_VariableRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		          83,500,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_DebtInstrumentAxis
= nsa_VariableRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
Effective interest rate     4.69%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= nsa_VariableRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		           
Minimum effective interest rate     2.43%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMinimum
/ us-gaap_DebtInstrumentAxis
= nsa_VariableRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		           
Maximum effective interest rate     9.65%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMaximum
/ us-gaap_DebtInstrumentAxis
= nsa_VariableRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember 		           
Mortgages [Member] | Variable Rate Mortgages [Member] | Subsequent Event [Member]                  
Debt Instrument [Line Items]                  
Repayment of long term debt             $ 83,500,000us-gaap_RepaymentsOfLongTermDebt
/ us-gaap_DebtInstrumentAxis
= nsa_VariableRateMortgagesMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember