Segment Information - Schedule of Financial Information of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 335,801	$ 337,505	$ 323,602	$ 311,546	$ 307,353	$ 306,953	$ 296,813	$ 285,485	$ 1,308,454	$ 1,196,604	$ 1,105,009
Operating expenses	171,156	174,867	165,609	163,069	150,676	153,362	152,097	151,573	674,701	607,708	563,404
Net operating income	164,645	162,638	157,993	148,477	156,677	153,591	144,716	133,912	634,958	619,703	654,394
Property management fees and other income									49,890	41,757	39,379
General and administrative expense									(89,418)	(81,256)	(78,961)
Depreciation and amortization expense									(219,857)	(209,050)	(193,296)
Gain on real estate transactions and impairment of real estate									1,205	30,807	112,789
Interest expense									(186,526)	(178,436)	(153,511)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes									(4,742)	(4,687)	(5,103)
Interest income									7,467	5,292	6,736
Equity in earnings of unconsolidated real estate entities									11,274	14,452	15,331
Income tax expense									(11,308)	(9,244)	(3,625)
Net income	$ 120,279	$ 115,995	$ 112,689	$ 102,160	$ 109,250	$ 139,687	$ 102,713	$ 95,430	451,123	447,080	514,222
Operating Segments
Segment Reporting Information [Line Items]
Revenues									1,258,564	1,154,847	1,065,630
Operating expenses									365,426	317,402	291,147
Net operating income									893,138	837,445	774,483
Operating Segments | Self-Storage Operations
Segment Reporting Information [Line Items]
Revenues									1,130,177	1,039,340	967,229
Operating expenses									336,050	291,695	271,974
Net operating income									794,127	747,645	695,255
Operating Segments | Tenant Reinsurance
Segment Reporting Information [Line Items]
Revenues									128,387	115,507	98,401
Operating expenses									29,376	25,707	19,173
Net operating income									$ 99,011	$ 89,800	$ 79,228