Consolidated Statements of Equity (USD $) In Thousands, except Share data, unless otherwise specified	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]	Total
Balances at Dec. 31, 2010	$ 25,000	$ 3	$ 1,515,468	$ (313,308)	$ (77,217)	$ 205,068	$ 1,355,014
Balances (in shares) at Dec. 31, 2010	1,000,000	31,325,000
Net income	0	0	0	47,070	0	10,446	57,516
Reversal of unrealized gains upon the sale of marketable securities	0	0	0	0	(4,011)	(275)	(4,286)
Changes in fair value of cash flow hedges and amortization of settlement swaps	0	0	0	0	7,212	495	7,707
Changes in fair value of marketable securities	0	0	0	0	1,245	85	1,330
Issuance of common stock under:
Stock option plans	0	0	8,412	0	0	0	8,412
Stock option plans (in shares)	0	103,000
Sale of common stock	0	0	323,931	0	0	0	323,931
Sale of common stock (in shares)	0	2,460,000
Equity based compensation costs	0	0	(725)	0	0	1,598	873
Issuance of Series H Preferred	73,750	0	(2,541)	0	0	0	71,209
Issuance of Series H Preferred (in shares)	2,950,000	0
Redemptions of Series F Preferred	(25,000)	0	0	0	0	0	(25,000)
Redemptions of Series F Preferred (in shares)	(1,000,000)	0
Redemptions of Series B Preferred	0	0	1,200	0	0	(80,000)	(78,800)
Redemptions of noncontrolling interest	0	0	(1,134)	0	0	(4,253)	(5,387)
Distributions to noncontrolling interest	0	0	0	0	0	(16,963)	(16,963)
Common and preferred stock dividends declared	0	0	0	(141,828)	0	0	(141,828)
Balances at Dec. 31, 2011	73,750	3	1,844,611	(408,066)	(72,771)	116,201	1,553,728
Balances (in shares) at Dec. 31, 2011	2,950,000	33,888,000
Net income	0	0	0	125,284	0	14,306	139,590
Reversal of unrealized gains upon the sale of marketable securities	0	0	0	0	(1,018)	(64)	(1,082)
Changes in fair value of cash flow hedges and amortization of settlement swaps	0	0	0	0	3,183	219	3,402
Changes in fair value of marketable securities	0	0	0	0	1,345	66	1,411
Issuance of common stock under:
Stock option plans	0	0	4,675	0	0	0	4,675
Stock option plans (in shares)	0	151,000
Sale of common stock	0	0	357,720	0	0	0	357,720
Sale of common stock (in shares)	0	2,404,000
Equity based compensation costs	0	0	(430)	0	0	2,231	1,801
Contributions of noncontrolling interest	0	0	0	0	0	4,232	4,232
Redemptions of noncontrolling interest	0	0	(1,798)	0	0	(5,188)	(6,986)
Distributions to noncontrolling interest	0	0	0	0	0	(16,691)	(16,691)
Common and preferred stock dividends declared	0	0	0	(161,684)	0	0	(161,684)
Balances at Dec. 31, 2012	73,750	3	2,204,778	(444,466)	(69,261)	115,312	1,880,116
Balances (in shares) at Dec. 31, 2012	2,950,000	36,443,000
Net income	0	0	0	156,283	0	15,772	172,055
Reversal of unrealized gains upon the sale of marketable securities	0	0	0	0	(1,673)	(94)	(1,767)
Changes in fair value of cash flow hedges and amortization of settlement swaps	0	0	0	0	11,934	680	12,614
Changes in fair value of marketable securities	0	0	0	0	(1,472)	(84)	(1,556)
Issuance of common stock under:
Stock option plans	0	0	7,244	0	0	0	7,244
Stock option plans (in shares)	0	65,000
Sale of common stock	0	1	138,365	0	0	0	138,366
Sale of common stock (in shares)	0	913,000
Equity based compensation costs	0	0	(907)	0	0	2,515	1,608
Redemptions of noncontrolling interest	0	0	(3,717)	0	0	(1,994)	(5,711)
Distributions to noncontrolling interest	0	0	0	0	0	(18,488)	(18,488)
Common and preferred stock dividends declared	0	0	0	(186,243)	0	0	(186,243)
Balances at Dec. 31, 2013	$ 73,750	$ 4	$ 2,345,763	$ (474,426)	$ (60,472)	$ 113,619	$ 1,998,238
Balances (in shares) at Dec. 31, 2013	2,950,000	37,421,000