Investment in Storage Facilities and Intangible Assets - Summary of Activity in Storage Facilities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Cost:
Beginning balance	$ 4,321,410
Improvements and equipment additions	3,497
Net increase in construction in progress	5,336
Dispositions	(1,984)
Ending balance	4,328,259
Accumulated Depreciation:
Beginning balance	624,314
Additions during the period	24,731
Dispositions	(1,915)
Ending balance	$ 647,130