Investment in Storage Facilities - Summary of Activity in Storage Facilities (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($)
Cost:
Beginning balance	$ 2,177,983
Acquisition of storage facilities	207,837
Improvements and equipment additions	12,197
Net increase in construction in progress	165
Dispositions	(1,744)
Ending balance	2,396,438
Accumulated Depreciation:
Beginning balance	411,701
Depreciation expense during the period	26,788
Dispositions	(1,023)
Ending balance	$ 437,466