Quarterly report pursuant to Section 13 or 15(d)

SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details)

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SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details)
$ / shares in Units, $ in Millions
 3 Months Ended
Mar. 16, 2023
USD ($)
property
shares
Mar. 15, 2023
shares
Feb. 27, 2019
USD ($)
$ / shares
Mar. 31, 2023
USD ($)
property
$ / shares
shares
Mar. 31, 2022
shares
Dec. 31, 2022
$ / shares
Jul. 11, 2022
USD ($)
May 19, 2021
USD ($)
Class of Stock [Line Items]                
Common shares of beneficial interest, par value (in dollars per share) | $ / shares     $ 0.01 $ 0.01   $ 0.01    
Authorized amount | $             $ 400.0  
Repurchase of common shares (in shares)       (1,622,874,000)        
Stock repurchased | $       $ 69.3        
Number of self storage properties | property       1,117        
Common Shares                
Class of Stock [Line Items]                
Repurchase of common shares (in shares)       (1,622,874)        
Redemptions/conversions of units (in shares)       67,431 258,477      
Series A Preferred Shares | NSA OP, LP                
Class of Stock [Line Items]                
Preferred share/unit dividend rate (percent)   6.00%            
Series B Preferred Shares                
Class of Stock [Line Items]                
Shares tied to promissory note (in shares) 1,059,683              
Series B Preferred Shares | Personal Mini                
Class of Stock [Line Items]                
Series B preferred shares | $ $ 139.6              
Number of self storage properties | property 15              
Notes receivable | $ $ 26.1              
Series B preferred shares value | $ 26.1              
Proceeds from issuance of preferred stock | $ $ 113.3              
Issuance of shares/units (in shares) 5,668,128              
Series B Preferred Shares | NSA OP, LP                
Class of Stock [Line Items]                
Preferred share/unit dividend rate (percent)   6.00%            
Preferred shares of beneficial interest, authorized (in shares)   7,000,000            
Preferred units stated value (in dollars per share) | $ / shares       $ 25.00        
OP units | NSA OP, LP                
Class of Stock [Line Items]                
Unit conversion ratio       1        
Minimum conversion period (in years)       1 year        
Issuance of shares/units (in shares)       2,545,063        
OP units | NSA OP, LP | Common Shares                
Class of Stock [Line Items]                
Redemptions/conversions of units (in shares)       67,431        
OP units | NSA OP, LP | Northwest Retirement                
Class of Stock [Line Items]                
Issuance of shares/units (in shares)       481,811        
OP units | NSA OP, LP | Retirement of Northwest                
Class of Stock [Line Items]                
Issuance of shares/units (in shares)       2,545,063        
OP units | DownREIT Partnership                
Class of Stock [Line Items]                
Unit conversion ratio       1        
Minimum conversion period (in years)       5 years        
Issuance of shares/units (in shares)       195,573        
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]                
Issuance of shares/units, non-voluntary (in shares)       926,623        
Redemptions/conversions of units (in shares)       926,623        
Unit conversion, lock out period (in years)       2 years        
Subordinated performance units | NSA OP, LP | Northwest Retirement                
Class of Stock [Line Items]                
Redemptions/conversions of units (in shares)       397,000        
Subordinated performance units | NSA OP, LP | Retirement of Northwest                
Class of Stock [Line Items]                
Issuance of shares/units (in shares)       701,646        
Subordinated performance units | DownREIT Partnership                
Class of Stock [Line Items]                
Unit conversion ratio       1        
Minimum conversion period (in years)       5 years        
Subordinated performance units | Personal Mini Affiliate | Personal Mini                
Class of Stock [Line Items]                
Payments to acquire interest in subsidiaries and affiliates | $ $ 26.1              
LTIP units | NSA OP, LP                
Class of Stock [Line Items]                
Unit conversion ratio       1        
Issuance of shares/units (in shares)       113,704        
Conversion of units (in shares)       85,696        
Series A-1 preferred units | NSA OP, LP                
Class of Stock [Line Items]                
Preferred share/unit dividend rate (percent)       6.00%        
Unit conversion ratio       1        
Issuance of series A-1 preferred units (in shares)       33,441        
DownREIT Subordinated Performance Performance Units | NSA OP, LP                
Class of Stock [Line Items]                
Conversion of stock (in shares)       203,637        
Prior Sales Agreement                
Class of Stock [Line Items]                
Value of common and preferred shares authorized under ATM program | $     $ 250.0          
Preferred share/unit dividend rate (percent)     6.00%          
At The Market Program                
Class of Stock [Line Items]                
Value of common and preferred shares authorized under ATM program | $               $ 400.0
Value of remaining available offered shares | $       $ 169.1       $ 31.0
Series A preferred shares | NSA OP, LP                
Class of Stock [Line Items]                
Preferred units cash redemption price (in dollars per share) | $ / shares       $ 25.00