Annual report pursuant to Section 13 and 15(d)

Investment in Storage Facilities - Summary of Activity in Storage Facilities (Detail)

v3.8.0.1
Investment in Storage Facilities - Summary of Activity in Storage Facilities (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Cost:    
Beginning balance $ 4,243,308 $ 2,491,702
Acquisition of storage facilities 22,638 1,714,029
Improvements and equipment additions 84,332 65,860
Net (decrease) increase in construction in progress (141) 7,525
Dispositions (28,727) (35,808)
Ending balance 4,321,410 4,243,308
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]    
Beginning balance 535,704 465,195
Additions during the year 102,674 87,219
Dispositions (14,064) (16,710)
Ending balance $ 624,314 $ 535,704