Segment Information - Schedule of Financial Information of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 281,842	$ 284,156	$ 276,003	$ 263,008	$ 261,016	$ 257,183	$ 244,273	$ 229,403	$ 1,105,009	$ 991,875	$ 782,270
Cost of operations	140,728	144,275	139,596	138,805	137,832	134,459	133,971	135,775	563,404	542,037	487,614
Total segment net operating income	141,114	139,881	136,407	124,203	123,184	122,724	110,302	93,628	541,605	449,838	294,656
General and administrative expense									(78,961)	(81,806)	(67,758)
Gain (loss) on real estate transactions, earnout from prior acquisition and sale of other assets									112,789	8,465	1,501
Interest expense									(153,511)	(133,479)	(95,682)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes									(5,103)	(4,980)	(3,310)
Interest income									3,801	6,148	3,461
Interest income on note receivable from Preferred Operating Partnership unit holder									2,935	4,850	4,850
Equity in earnings of unconsolidated real estate ventures									15,331	12,895	12,351
Equity in earnings of unconsolidated real estate ventures - gain on sale of real estate assets and purchase of partners' interests									0	69,199	2,857
Income tax expense									(3,625)	(15,847)	(11,148)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 229,315	$ 101,075	$ 94,098	$ 89,734	$ 90,416	$ 127,226	$ 90,040	$ 89,407	514,222	397,089	209,536
Operating Segments
Segment Reporting Information [Line Items]
Revenues									1,065,630	952,033	748,109
Cost of operations									291,147	265,560	216,998
Total segment net operating income									774,483	686,473	531,111
Property management fees and other income									39,379	39,842	34,161
General and administrative expense									(78,961)	(81,806)	(67,758)
Depreciation and amortization expense									(193,296)	(182,560)	(133,457)
Acquisition and other related costs									0	(12,111)	(69,401)
Gain (loss) on real estate transactions, earnout from prior acquisition and sale of other assets									112,789	8,465	1,501
Interest expense									(153,511)	(133,479)	(95,682)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes									(5,103)	(4,980)	(3,310)
Interest income									3,801	6,148	3,461
Interest income on note receivable from Preferred Operating Partnership unit holder									2,935	4,850	4,850
Equity in earnings of unconsolidated real estate ventures									15,331	12,895	12,351
Equity in earnings of unconsolidated real estate ventures - gain on sale of real estate assets and purchase of partners' interests									0	69,199	2,857
Income tax expense									(3,625)	(15,847)	(11,148)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest									514,222	397,089	209,536
Operating Segments | Self-storage operations
Segment Reporting Information [Line Items]
Revenues									967,229	864,742	676,138
Cost of operations									271,974	250,005	203,965
Total segment net operating income									695,255	614,737	472,173
Operating Segments | Tenant reinsurance
Segment Reporting Information [Line Items]
Revenues									98,401	87,291	71,971
Cost of operations									19,173	15,555	13,033
Total segment net operating income									$ 79,228	$ 71,736	$ 58,938