Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Distributions in Excess of Accumulated Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]
Balances at Dec. 31, 2012	$ 1,880,116	$ 73,750	$ 3	$ 2,204,778	$ (444,466)	$ (69,261)	$ 115,312
Balances (in shares) at Dec. 31, 2012		2,950	36,443
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	172,055				156,283		15,772
Reversal of unrealized gains upon the sale of marketable securities	(1,767)					(1,673)	(94)
Changes in fair value of cash flow hedges and reclassification to interest expense	12,614					11,934	680
Changes in fair value of marketable securities	(1,556)					(1,472)	(84)
Issuance of common stock under:
Stock option plans	7,244			7,244
Stock option plans (in shares)			65
Sale of common stock	138,366		$ 1	138,365
Sale of common stock (in shares)			913
Equity-based compensation costs	1,608			(907)			2,515
Redemptions of noncontrolling interest	(5,711)			(3,717)			(1,994)
Distributions to noncontrolling interest	(18,488)						(18,488)
Contributions from noncontrolling interest	0
Retirement of noncontrolling interest	0
Common and preferred stock dividends	(186,243)				(186,243)
Balances at Dec. 31, 2013	1,998,238	$ 73,750	$ 4	2,345,763	(474,426)	(60,472)	113,619
Balances (in shares) at Dec. 31, 2013		2,950	37,421
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	134,438				122,150		12,288
Reversal of unrealized gains upon the sale of marketable securities	(886)					(841)	(45)
Changes in fair value of cash flow hedges and reclassification to interest expense	4,168					3,721	447
Changes in fair value of marketable securities	6,302					6,140	162
Issuance of common stock under:
Stock option plans	3,774,087		$ 2	3,774,085
Stock option plans (in shares)			23,067
Stock option and restricted stock plans	11,024			11,024
Stock option and restricted stock plans (in shares)			218
Sale of common stock	532,670			532,670
Sale of common stock (in shares)			2,943
Equity-based compensation costs	11,872			5,719			6,153
Redemptions of noncontrolling interest	(4,026)			(2,934)			(1,092)
Distributions to noncontrolling interest	(17,069)						(17,069)
Reclassification of noncontrolling interest to redeemable noncontrolling interest	(20,890)			(19,823)			(1,067)
Changes in the redemption value of redeemable noncontrolling interest	312			312
Conversion of Series G preferred stock	4,349			4,349
Conversion of Series G preferred stock (in shares)			34
Contributions from noncontrolling interest	(1,419,816)						(1,419,816)
Retirement of noncontrolling interest	(1,419,816)						(1,419,816)
Common and preferred stock dividends	(298,521)				(298,521)
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	63,683
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
Changes in fair value of cash flow hedges and reclassification to interest expense	7,893					7,637	256
Changes in fair value of marketable securities	1,865					1,804	61
Issuance of common stock under:
Stock option and restricted stock plans	26,540			26,540
Stock option and restricted stock plans (in shares)			207
Sale of common stock	332,137			332,137
Sale of common stock (in shares)			1,489
Equity-based compensation costs	9,646			5,946			3,700
Redemptions of noncontrolling interest	(2,621)			(2,199)			(422)
Distributions to noncontrolling interest	(21,705)						(21,705)
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)
Contributions from noncontrolling interest	0
Retirement of noncontrolling interest	0
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	65,379