Consolidated Statement of Changes in Stockholders' Equity and Noncontrolling Interests (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Series D Cumulative Convertible Preferred Stock	Series E Cumulative Redeemable Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests	Redeemable Noncontrolling Interests
Beginning balance at Dec. 31, 2012	$ 3,488,494	$ 250,000	$ 130,000	$ 632	$ 3,086,052	$ 0	$ (24,833)	$ 46,643	$ 14,564
Beginning balance (in shares) at Dec. 31, 2012				63,244,645
Increase (Decrease) in Stockholders' Equity
Net income	95,223					93,105		2,118	804
Total other comprehensive income (loss)	(15,276)						(15,193)	(83)	0
Distributions to noncontrolling interests	(1,207)							(1,207)	(893)
Issuance of common stock (in shares)				7,590,000
Issuance of common stock	534,677			76	534,601
Issuances pursuant to stock plan (in shares)				246,283
Issuances pursuant to stock plan	17,390			3	17,387
Dividends declared on common stock	(133,388)					(133,388)
Dividends declared on preferred stock	(19,414)					(19,414)
Distributions in excess of earnings					(59,697)	59,697
Ending balance at Sep. 30, 2013	$ 3,966,499	$ 250,000	$ 130,000	$ 711	$ 3,578,343	$ 0	$ (40,026)	$ 47,471	$ 14,475
Ending balance (in shares) at Sep. 30, 2013				71,080,928