Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 514,222	$ 397,089	$ 209,536
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	193,296	182,560	133,457
Amortization of deferred financing costs	12,289	12,922	7,779
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	5,103	4,980	3,310
Non-cash interest expense related to amortization of premium on notes payable	0	(872)	(2,409)
Compensation expense related to stock-based awards	9,561	8,045	6,055
Gain on sale of real estate assets and purchase of joint venture partners' interests	0	(69,199)	(2,857)
Gain on real estate transactions, earnout from prior acquisition and impairment of real estate	(112,789)	(8,465)	(1,501)
Distributions from unconsolidated real estate ventures in excess of earnings	4,567	3,534	4,531
Changes in operating assets and liabilities:
Receivables from related parties and affiliated real estate joint ventures	1,966	1,367	(1,436)
Other assets	(14,694)	(2,981)	(1,172)
Accounts payable and accrued expenses	(10,515)	10,075	108
Other liabilities	(5,631)	208	11,928
Net cash provided by operating activities	597,375	539,263	367,329
Cash flows from investing activities:
Acquisition of real estate assets	653,185	1,086,523	349,897
Development and redevelopment of real estate assets	(31,746)	(23,279)	(26,931)
Acquisition of SmartStop, net of cash acquired	0	0	(1,200,853)
Proceeds from sale of real estate assets, investments in real estate ventures and other assets	312,165	60,813	800
Change in restricted cash	(16,477)	16,854	1,282
Investment in unconsolidated real estate ventures	(17,944)	(28,241)	(3,434)
Return of investment in unconsolidated real estate ventures	581	16,953	45,080
Purchase/issuance of notes receivable	0	(26,429)	(84,331)
Principal payments received from notes receivable	44,869	42,785	0
Purchase of equipment and fixtures	(7,819)	(4,968)	(7,380)
Net cash used in investing activities	(369,556)	(1,032,035)	(1,625,664)
Cash flows from financing activities:
Proceeds from the sale of common stock, net of offering costs	0	123,424	446,877
Proceeds from notes payable and revolving lines of credit	1,325,623	1,900,357	2,121,802
Principal payments on notes payable and revolving lines of credit	(1,088,679)	(1,122,442)	(1,313,570)
Deferred financing costs	(6,967)	(17,486)	(9,779)
Net proceeds from the issuance of 2015 exchangeable senior notes	0	0	563,500
Repurchase of exchangeable senior notes	(19,916)	(22,195)	(227,212)
Net proceeds from exercise of stock options	1,266	1,444	1,542
Proceeds from termination of interest rate cap	0	1,650	0
Purchase of interest rate cap	0	0	(2,884)
Payment of earnout from prior acquisition	0	(4,600)	0
Redemption of Operating Partnership units held by noncontrolling interests	(2,510)	(506)	0
Contributions from noncontrolling interests	201	0	0
Dividends paid on common stock	(393,040)	(367,818)	(269,302)
Distributions to noncontrolling interests	(31,972)	(30,997)	(24,503)
Net cash provided by (used in) financing activities	(215,994)	460,831	1,286,471
Net increase (decrease) in cash and cash equivalents	11,825	(31,941)	28,136
Cash and cash equivalents, beginning of the period	43,858	75,799	47,663
Cash and cash equivalents, end of the period	55,683	43,858	75,799
Supplemental schedule of cash flow information
Interest paid	136,202	122,265	89,507
Income taxes paid	5,648	14,864	1,782
Redemption of Operating Partnership units held by noncontrolling interests for common stock
Noncontrolling interests in Operating Partnership	0	(577)	(28,106)
Common stock and paid-in capital	0	577	28,106
Tax effect from vesting of restricted stock grants and option exercises
Other assets	0	2,404	1,727
Additional paid-in capital	0	(2,404)	(1,727)
Acquisitions of real estate assets
Real Estate Assets	627,462	1,149,936
Notes payable assumed	(24,055)	(9,723)
Investment in unconsolidated real estate ventures	(12,957)	0	0
Accrued construction costs and capital expenditures
Acquisition of real estate assets	3,509	8,497	2,332
Development and redevelopment of real estate assets	1,703	125	0
Accounts payable and accrued expenses	(5,212)	(8,622)	(2,332)
Distribution of real estate from investments in unconsolidated real estate ventures
Real estate assets, net	0	25,055	0
Investments in unconsolidated real estate ventures	0	(25,055)	0
Disposition of real estate assets
Real estate assets, net	0	(7,689)	0
Issuance of Preferred OP Units for additional investment in unconsolidated real estate venture
Preferred OP Units issued	(4,351)	0	0
Investment in unconsolidated real estate ventures	4,351	0	0
Acquisitions of real estate assets
Acquisitions of real estate assets
Real Estate Assets	51,455	84,163	158,009
Value of Operating Partnership units issued	(14,428)	(74,440)	(142,399)
Notes payable assumed	(24,055)	(9,723)	0
Receivables from related parties and affiliated real estate joint ventures	0	0	(15,610)
Other noncontrolling interests	(15)	0	0
Operating Partnership units redeemed
Disposition of real estate assets
Operating Partnership units redeemed	0	7,689	0
Acquisition of noncontrolling interests
Acquisition of noncontrolling interests
Operating Partnership units issued	0	(800)	0
Other noncontrolling interests	0	162	0
Additional paid-in capital	$ 0	$ 638	$ 0