Investment in Storage Facilities and Intangible Assets - Summary of Activity in Storage Facilities (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Cost:
Beginning balance	$ 4,321,410
Improvements and equipment additions	14,123
Net increase in construction in progress	14,040
Dispositions	(2,189)
Ending balance	4,347,384
Accumulated Depreciation:
Beginning balance	624,314
Additions during the period	49,557
Dispositions	(2,154)
Ending balance	$ 671,717