CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2013
Dec. 31, 2015
Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES        
Net income (loss)   $ (10,481) $ 4,796 $ (16,357)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:        
Depreciation and amortization   8,403 40,651 23,785
Amortization of debt issuance costs   1,291 2,714 3,282
Amortization of debt discount and premium, net   3,229 (1,747) 495
Loss on debt extinguishment   0 414 344
Unrealized loss (gain) on fair value of derivatives   (245) 68 332
Gain on sale of self storage properties   0 0 (1,427)
Issuance of subordinated performance units for related party payable   0 0 2,994
LTIP units issued for acquisition expenses   0 1,020 1,460
Equity-based compensation expense   1,104 3,027 1,468
Change in assets and liabilities, net of effects of business combinations:        
Restricted cash   (244) 1,076 1,051
Other assets   705 (680) (271)
Accounts payable and accrued liabilities   2,129 269 (126)
Deferred revenue   (103) (198) (607)
Net Cash Provided by Operating Activities   5,788 51,410 16,423
CASH FLOWS FROM INVESTING ACTIVITIES        
Acquisition of self storage properties   (103,828) (171,822) (217,939)
Capital expenditures   (2,188) (4,072) (3,843)
Note receivable from PROs   0 0 (12,813)
Deposits and advances for self storage property acquisitions   0 (738) (913)
Expenditures for corporate furniture, equipment and other   0 (418) (146)
Change in restricted cash designated for capital expenditures   180 141 662
Proceeds from sale of self storage properties   0 0 2,993
Cash acquired in reorganization of entities under common control   3,469 0 0
Net Cash (Used in) Provided By Investing Activities   (102,367) (176,909) (231,999)
CASH FLOWS FROM FINANCING ACTIVITIES        
Proceeds from issuance of common shares in IPO   0 278,070 0
Borrowings under debt financings   150,372 258,443 372,839
Proceeds from issuance of OP units and subordinated performance units   6,281 0 438
Receipts for OP unit subscriptions   5,863 1,015 0
Collection of receivables from issuance of OP equity   0 774 89
Principal payments under debt financings   (48,048) (357,273) (143,970)
Payment of dividends to common shareholders   0 (12,429) 0
Distributions to noncontrolling interests   (2,192) (37,992) (12,567)
NSA Predecessor distributions and other   (1,641) 0 34
Change in restricted cash for financing activity   0 (167) 0
Debt issuance costs   (2,495) (1,848) (1,774)
Equity offering costs   (365) (5,438) (1,700)
Net Cash Provided by (Used In) Financing Activities   107,775 123,155 213,389
(Decrease) Increase in Cash and Cash Equivalents   11,196 (2,344) (2,187)
CASH AND CASH EQUIVALENTS        
Beginning of period   0 9,009 11,196
End of period $ 0 11,196 6,665 9,009
Supplemental Cash Flow Information        
Cash paid for interest   18,933 20,206 18,771
Consideration exchanged in business combinations:        
Issuance of OP units and subordinated performance units   83,568 42,113 137,017
Deposits on acquisitions applied to purchase price   0 745 0
LTIP units vesting upon acquisition of properties   2,918 1,402 3,652
Assumption of mortgages payable   4,461 73,498 65,816
Note payable to related party to settle assumed mortgages   0 5,342 0
Other net liabilities assumed   1,030 511 2,403
OP units in exchange for receivable from seller   220 0 5,206
Notes receivable settled upon acquisition of properties   0 1,778 11,035
Fair value of noncontrolling interests in acquired subsidiaries   0 21,137 41,297
Issuance of OP units for settlement of subscription liability   0 1,416 5,863
Settlement of acquisition receivables from distributions   0 1,473 105
Increase in lender participation liability and related discount   1,971 0 770
Increase in OP unit subscription liability through reduced distributions   0 498 0
(Decrease) increase in payables for deferred offering costs   0 (1,379) 1,418
Settlement of debt issuance costs from borrowings   1,966 0 3,763
Settlement of offering expenses from IPO proceeds   0 20,930 0
Contributions by NSA Predecessor in reorganization of entities under common control:        
Self storage properties, net   159,509 $ 304,500 $ 465,900
Restricted cash   2,567    
Debt issuance costs, net   816    
Other assets, net   795    
Mortgages and notes payable   (163,302)    
Participating mortgage payable   (23,467)    
Accounts payable and other accrued liabilities   (2,920)    
Deferred revenue   (1,242)    
Non-cash liabilities of NSA Predecessor in excess of assets   (27,244)    
NSA Predecessor [Member]        
CASH FLOWS FROM OPERATING ACTIVITIES        
Net income (loss) (1,253)      
Adjustments to reconcile net income (loss) to net cash provided by operating activities:        
Depreciation and amortization 972      
Amortization of debt issuance costs 167      
Amortization of debt discount and premium, net 1,421      
Loss on debt extinguishment 0      
Unrealized loss (gain) on fair value of derivatives (60)      
Gain on sale of self storage properties 0      
Issuance of subordinated performance units for related party payable 0      
LTIP units issued for acquisition expenses 0      
Equity-based compensation expense 0      
Change in assets and liabilities, net of effects of business combinations:        
Restricted cash (120)      
Other assets (205)      
Accounts payable and accrued liabilities 315      
Deferred revenue 109      
Net Cash Provided by Operating Activities 1,346      
CASH FLOWS FROM INVESTING ACTIVITIES        
Acquisition of self storage properties 0      
Capital expenditures (205)      
Note receivable from PROs 0      
Deposits and advances for self storage property acquisitions 0      
Expenditures for corporate furniture, equipment and other 0      
Change in restricted cash designated for capital expenditures 246      
Proceeds from sale of self storage properties 0      
Cash acquired in reorganization of entities under common control 0      
Net Cash (Used in) Provided By Investing Activities 41      
CASH FLOWS FROM FINANCING ACTIVITIES        
Proceeds from issuance of common shares in IPO 0      
Borrowings under debt financings 0      
Proceeds from issuance of OP units and subordinated performance units 0      
Receipts for OP unit subscriptions 0      
Collection of receivables from issuance of OP equity 0      
Principal payments under debt financings (628)      
Payment of dividends to common shareholders 0      
Distributions to noncontrolling interests 0      
NSA Predecessor distributions and other 0      
Change in restricted cash for financing activity 0      
Debt issuance costs 0      
Equity offering costs 0      
Net Cash Provided by (Used In) Financing Activities (628)      
(Decrease) Increase in Cash and Cash Equivalents 759      
CASH AND CASH EQUIVALENTS        
Beginning of period 2,769 $ 3,528    
End of period 3,528      
Supplemental Cash Flow Information        
Cash paid for interest 2,604      
Consideration exchanged in business combinations:        
Issuance of OP units and subordinated performance units 0      
Deposits on acquisitions applied to purchase price 0      
LTIP units vesting upon acquisition of properties 0      
Assumption of mortgages payable 0      
Note payable to related party to settle assumed mortgages 0      
Other net liabilities assumed 0      
OP units in exchange for receivable from seller 0      
Notes receivable settled upon acquisition of properties 0      
Fair value of noncontrolling interests in acquired subsidiaries 0      
Issuance of OP units for settlement of subscription liability 0      
Settlement of acquisition receivables from distributions 0      
Increase in lender participation liability and related discount 767      
Increase in OP unit subscription liability through reduced distributions 0      
(Decrease) increase in payables for deferred offering costs 0      
Settlement of debt issuance costs from borrowings 0      
Settlement of offering expenses from IPO proceeds $ 0