Quarterly report pursuant to Section 13 or 15(d)

SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details)

v3.21.1
SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended
Mar. 22, 2021
Dec. 30, 2020
Oct. 06, 2020
Sep. 22, 2020
Feb. 27, 2019
Oct. 06, 2020
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Class of Stock [Line Items]                  
Common shares of beneficial interest, par value (in dollars per share)       $ 0.01     $ 0.01   $ 0.01
Value of common and preferred shares authorized under ATM program         $ 250,000,000.0        
Preferred share/unit dividend rate (percent)         6.00%        
Proceeds from issuance of common shares             $ 122,412,000 $ 4,249,000  
Preferred units stated value (in dollars per share)             $ 0.01   0.01
Common Shares                  
Class of Stock [Line Items]                  
Issuance of shares/units (in shares)               125,000  
Redemptions/conversions of units (in shares)             190,248 118,961  
Series A-1 preferred units | NSA OP, LP                  
Class of Stock [Line Items]                  
Preferred share/unit dividend rate (percent)             6.00%    
Preferred units stated value (in dollars per share)             $ 25.00    
Unit conversion ratio             1    
OP units | NSA OP, LP                  
Class of Stock [Line Items]                  
Issuance of shares/units (in shares)             63,033    
Unit conversion ratio             1    
Minimum conversion period (in years)             1 year    
OP units | NSA OP, LP | Common Shares                  
Class of Stock [Line Items]                  
Redemptions/conversions of units (in shares)             190,248    
OP units | NSA OP, LP | Self Storage Properties                  
Class of Stock [Line Items]                  
Issuance of shares/units (in shares)             351,457    
OP units | DownREIT Partnership                  
Class of Stock [Line Items]                  
Unit conversion ratio             1    
Minimum conversion period (in years)             5 years    
LTIP units | NSA OP, LP                  
Class of Stock [Line Items]                  
Issuance of shares/units (in shares)             144,592    
Unit conversion ratio             1    
Conversion of units (in shares)             80,006    
Subordinated performance units                  
Class of Stock [Line Items]                  
Time frame prior to conversion for conversion metric (in years)             1 year    
Percentage of cash available for distribution used in conversion ratio calculation             110.00%    
Subordinated performance units | NSA OP, LP                  
Class of Stock [Line Items]                  
Redemptions/conversions of units (in shares)             32,741    
Unit conversion, lock out period (in years)             2 years    
Subordinated performance units | NSA OP, LP | Self Storage Properties                  
Class of Stock [Line Items]                  
Issuance of shares/units (in shares)             199,128    
Subordinated performance units | DownREIT Partnership                  
Class of Stock [Line Items]                  
Unit conversion ratio             1    
Minimum conversion period (in years)             5 years    
Common shares | Common Shares                  
Class of Stock [Line Items]                  
Issuance of shares/units (in shares)             3,692,216    
Common shares | Public Stock Offering                  
Class of Stock [Line Items]                  
Sale of stock, number of shares issued in transaction (in shares)       4,500,000          
Sale of stock, price per share (in dollars per share)       $ 33.15          
Sale of stock, additional number of shares issued in transaction (in shares)     400,000            
Common shares | Public Stock Offering - From Third Parties                  
Class of Stock [Line Items]                  
Sale of stock, number of shares issued in transaction (in shares) 3,049,490 1,850,510       4,900,000      
Sale of stock, price per share (in dollars per share)     $ 33.15     $ 33.15      
Sale of stock, consideration received on transaction $ 97,300,000 $ 60,000,000.0       $ 162,400,000      
Common shares | At the Market Program                  
Class of Stock [Line Items]                  
Issuance of shares/units (in shares)             642,726    
Average offering price (in dollars per share)             $ 39.41    
Proceeds from issuance of common shares             $ 25,100,000    
Underwriter option to purchase | Public Stock Offering                  
Class of Stock [Line Items]                  
Sale of stock, number of shares issued in transaction (in shares)       675,000          
Series A preferred shares | NSA OP, LP                  
Class of Stock [Line Items]                  
Preferred units cash redemption price (in dollars per share)                 $ 25.00