Subsequent Events - Carrying Amounts of Major Classes of Assets and Liabilities Related to Self Storage Facilities (Detail) - USD ($) $ in Thousands	Jul. 02, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Subsequent Event [Line Items]
Land		$ 831,478	$ 794,729
Building, equipment, and construction in progress		3,710,133	3,604,210
Accumulated depreciation		753,581	704,681
Cash and cash equivalents		46,058	13,560	$ 7,327
Accounts receivable		9,711	7,805
Other assets		30,378	5,921
Accounts payable and accrued liabilities		90,344	87,446
Deferred revenue		$ 9,411	$ 9,191
Subsequent Event [Member] | Self-storage Facilities [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Subsequent Event [Line Items]
Land	$ 21,816
Building, equipment, and construction in progress	132,415
Accumulated depreciation	45,515
Cash and cash equivalents	110
Accounts receivable	118
Other assets	56
Accounts payable and accrued liabilities	1,030
Deferred revenue	$ 361