Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Additional Information (Detail)

v3.8.0.1
Fair Value Measurements - Additional Information (Detail) - Property
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Number of storage facilities acquired 2 122
Storage Facilities [Member]    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Number of storage facilities acquired 0