Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Series H Preferred Stock [Member]	Common Stock [Member]	Additional paid-in capital [Member]	Distributions in excess of accumulated earnings [Member]	Accumulated other comprehensive loss, net [Member]	Noncontrolling Interest [Member]
Balances at Dec. 31, 2014	$ 6,136,068	$ 73,750	$ 6	$ 6,651,165	$ (650,797)	$ (51,452)	$ 113,396
Balances (in shares) at Dec. 31, 2014		2,950,000	63,683,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	248,239				232,120		16,119
Reversal of unrealized gains upon the sale of marketable securities	0
Change in fair value of derivatives and amortization of swap settlements	7,893					7,637	256
Changes in fair value of marketable securities, net	1,865					1,804	61
Issuance of common stock under:
Stock option and restricted stock plans, net	26,540			26,540
Stock option and restricted stock plans, net (in shares)			207,000
Sale of common stock, net	332,137			332,137
Sale of common stock, net (in shares)			1,482,000
Equity based compensation costs	9,646			5,946			3,700
Reclassification of noncontrolling interest to redeemable noncontrolling interest	(19,772)			(7,657)			(12,115)
Changes in the redemption value of redeemable noncontrolling interest	(2,615)			(2,615)
Distributions to noncontrolling interest	(21,705)						(21,705)
Redemptions of noncontrolling interest	(2,621)			(2,199)			(422)
Redemptions of noncontrolling interest (in shares)			7,000
Common and preferred stock dividends	(378,652)				(378,652)
Balances at Dec. 31, 2015	6,337,023	$ 73,750	$ 6	7,003,317	(797,329)	(42,011)	99,290
Balances (in shares) at Dec. 31, 2015		2,950,000	65,379,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	438,410				414,979		23,431
Reversal of unrealized gains upon the sale of marketable securities	(4,848)					(4,689)	(159)
Change in fair value of derivatives and amortization of swap settlements	15,926					15,403	523
Changes in fair value of marketable securities, net	(828)					(801)	(27)
Issuance of common stock under:
Stock option and restricted stock plans, net	18,949			18,949
Stock option and restricted stock plans, net (in shares)			140,000
Sale of common stock, net	$ (384)			(384)
Sale of common stock, net (in shares)	0
Equity based compensation costs	$ 10,899			8,246			2,653
Redemption of Series H preferred stock	(73,750)	$ (73,750)		2,541	(2,541)
Redemption of Series H preferred stock (in shares)		(2,950,000)
Retirement of common stock, net	(1,045)			(1,045)
Retirement of common stock, net (in shares)			(5,000)
Changes in the redemption value of redeemable noncontrolling interest	768			172			596
Distributions to noncontrolling interest	(25,854)						(25,854)
Redemptions of noncontrolling interest	(2,511)			(2,117)			(394)
Redemptions of noncontrolling interest (in shares)			14,000
Common and preferred stock dividends	(420,518)				(420,518)
Balances at Dec. 31, 2016	6,292,237	$ 0	$ 6	7,029,679	(805,409)	(32,098)	100,059
Balances (in shares) at Dec. 31, 2016		0	65,528,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	458,043				433,059		24,984
Reversal of unrealized gains upon the sale of marketable securities	(1,909)					(1,846)	(63)
Change in fair value of derivatives and amortization of swap settlements	12,744					12,322	422
Changes in fair value of marketable securities, net	3,284					3,176	108
Issuance of common stock under:
Stock option and restricted stock plans, net	26,635			26,635
Stock option and restricted stock plans, net (in shares)			179,000
Sale of common stock, net	$ 89,055		$ 1	89,054
Sale of common stock, net (in shares)	345,444		345,000
Equity based compensation costs	$ 11,302			9,529			1,773
Changes in the redemption value of redeemable noncontrolling interest	(65)			(136)			71
Contributions from noncontrolling interest	22,506						22,506
Distributions to noncontrolling interest	(27,051)						(27,051)
Redemptions of noncontrolling interest	(28,580)			(25,190)			(3,390)
Redemptions of noncontrolling interest (in shares)			2,000
Common and preferred stock dividends	(461,376)				(461,376)
Balances at Dec. 31, 2017	$ 6,396,825	$ 0	$ 7	$ 7,129,571	$ (833,726)	$ (18,446)	$ 119,419
Balances (in shares) at Dec. 31, 2017		0	66,054,000