Segment Information - Schedule of Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenues:	$ 327,246		$ 323,602		$ 659,698	$ 635,148
Operating expenses:	177,253		165,609		352,514	328,678
Income from operations	149,993		159,198		307,184	307,675
Management fees and other income	12,856		12,317		24,992	23,063
General and administrative expense	(25,337)		(23,351)		(48,348)	(46,029)
Depreciation and amortization expense	(56,018)		(54,406)		(111,293)	(109,065)
Interest expense	(41,039)		(47,448)		(85,397)	(94,808)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(1,233)		(1,185)		(2,442)	(2,347)
Interest income	1,669		1,718		3,343	3,106
Equity in earnings and dividend income from unconsolidated real estate entities	5,044		3,121		10,087	5,751
Income tax expense	(3,177)		(2,715)		(5,356)	(4,528)
Net income	111,257	$ 116,162	112,689	$ 102,160	227,419	214,849
Operating Segments
Segment Reporting Information [Line Items]
Revenues:	314,390		311,285		634,706	612,085
Operating expenses:	95,898		87,852		192,873	173,584
Income from operations	218,492		223,433		441,833	438,501
Self-Storage Operations | Operating Segments
Segment Reporting Information [Line Items]
Revenues:	279,312		279,584		566,015	550,587
Operating expenses:	89,040		80,870		179,337	159,635
Income from operations	190,272		198,714		386,678	390,952
Tenant Reinsurance | Operating Segments
Segment Reporting Information [Line Items]
Revenues:	35,078		31,701		68,691	61,498
Operating expenses:	6,858		6,982		13,536	13,949
Income from operations	$ 28,220		$ 24,719		$ 55,155	$ 47,549