Segment Information - Schedule of Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues:	$ 332,452	$ 311,546
Operating expenses:	175,261	163,069
Income from operations	157,191	148,477
Property management fees and other income	12,136	10,746
General and administrative expense	(23,011)	(22,678)
Depreciation and amortization expense	(55,275)	(54,659)
Interest expense	(44,358)	(47,360)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(1,209)	(1,162)
Interest income	1,674	1,388
Equity in earnings and dividend income from unconsolidated real estate entities	5,043	2,630
Income tax expense	(2,179)	(1,813)
Net income	116,162	102,160
Operating Segments
Segment Reporting Information [Line Items]
Revenues:	320,316	300,800
Operating expenses:	96,975	85,732
Income from operations	223,341	215,068
Operating Segments | Self-Storage Operations
Segment Reporting Information [Line Items]
Revenues:	286,703	271,003
Operating expenses:	90,297	78,765
Income from operations	196,406	192,238
Operating Segments | Tenant Reinsurance
Segment Reporting Information [Line Items]
Revenues:	33,613	29,797
Operating expenses:	6,678	6,967
Income from operations	$ 26,935	$ 22,830