Segment Information - Schedule of Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues:	$ 358,857	$ 332,452
Operating expenses:	181,667	175,261
Net operating income:	241,073	157,191
Management fees and other income	15,645	12,136
General and administrative expense	(23,540)	(23,011)
Depreciation and amortization expense	(58,599)	(55,275)
Gain on real estate transactions	63,883	0
Interest expense	(40,695)	(44,358)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	0	(1,209)
Interest income	12,304	1,674
Equity in earnings and dividend income from unconsolidated real estate entities	6,956	5,043
Income tax expense	(4,137)	(2,179)
Net income	215,501	116,162
Operating Segments
Segment Reporting Information [Line Items]
Revenues:	343,212	320,316
Operating expenses:	99,528	96,975
Net operating income:	243,684	223,341
Self-Storage Operations | Operating Segments
Segment Reporting Information [Line Items]
Revenues:	303,593	286,703
Operating expenses:	92,367	90,297
Net operating income:	211,226	196,406
Tenant Reinsurance | Operating Segments
Segment Reporting Information [Line Items]
Revenues:	39,619	33,613
Operating expenses:	7,161	6,678
Net operating income:	$ 32,458	$ 26,935