Quarterly report pursuant to Section 13 or 15(d)

SELF STORAGE PROPERTY ACQUISITIONS - Business Combination Consideration (Details)

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SELF STORAGE PROPERTY ACQUISITIONS - Business Combination Consideration (Details) (USD $)
0 Months Ended 1 Months Ended 3 Months Ended
Jan. 01, 2015
property
Jan. 31, 2015
property
Mar. 31, 2015
property
Mar. 31, 2014
Business Combinations [Abstract]        
Number of self storage properties acquired 5us-gaap_NumberOfBusinessesAcquired 6us-gaap_NumberOfBusinessesAcquired 6us-gaap_NumberOfBusinessesAcquired  
Consideration given, cash     $ 6,991,000us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired $ 1,850,000us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired
Consideration given, value of OP Equity     8,954,000us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable  
Consideration given, settlement of note receivable     1,778,000nsa_BusinessCombinationConsiderationTransferredNotesReceivable  
Liabilities assumed, mortgages     16,442,000nsa_BusinessCombinationConsiderationTransferredLiabilitiesIncurredMortgages  
Liabilities assumed, other     70,000us-gaap_BusinessCombinationConsiderationTransferredOther1  
Total consideration given and liabilities assumed     34,235,000us-gaap_BusinessCombinationConsiderationTransferred1  
Business combination, noncontrolling interest, fair value     $ 6,800,000us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue