CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Distributions in Excess of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non-controlling Interests [Member]
Beginning balance at Dec. 31, 2011	$ 1,170,203	$ 311,673	$ 15	$ 2,010,850	$ (1,212,630)	$ 1,938	$ 58,357
Beginning balance (in shares) at Dec. 31, 2011		10,911,074	154,938,351
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions from noncontrolling interests	1,262						1,262
Redemption of noncontrolling OP units for common shares				1,343			(1,343)
Redemption of noncontrolling OP units for common shares (in shares)			257,427
Repurchase of preferred shares	(70,000)	(67,883)			(2,117)
Repurchase of preferred shares (in shares)		(2,775,674)
Issuance of common shares upon conversion of Convertible Notes	33,770		1	33,769
Issuance of common shares upon conversion of convertible notes (in shares)	4,487,060		4,487,060
Exercise of employee common share options, net	(534)			(534)
Exercise of employee common share options, net (in shares)			110,944
Issuance of common shares and deferred compensation amortization, net	167,523		2	167,521
Issuance of common shares and deferred compensation amortization, net (in shares)			18,822,882
Deconsolidation of consolidated joint venture	(782)						(782)
Dividends/distributions	(144,753)				(109,372)		(35,381)
Net income	184,638				180,316		4,322
Other comprehensive income (loss)	(8,162)					(8,162)
Ending balance at Dec. 31, 2012	1,333,165	243,790	18	2,212,949	(1,143,803)	(6,224)	26,435
Ending balance (in shares) at Dec. 31, 2012		8,135,400	178,616,664
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares				1,053			(1,053)
Redemption of noncontrolling OP units for common shares (in shares)			202,241
Repurchase of preferred shares	(155,004)	(149,774)			(5,230)
Repurchase of preferred shares (in shares)		(6,200,000)
Issuance of common shares upon conversion of Convertible Notes	60,686		1	60,685
Issuance of common shares upon conversion of convertible notes (in shares)	7,944,673		7,944,673
Acquisition of consolidated joint venture partner's equity interest	(8,918)				(8,918)
Exercise of employee common share options, net	2,289			2,289
Exercise of employee common share options, net (in shares)			955,478
Forfeiture of employee common shares	(20)			(20)
Forfeiture of employee common shares (in shares)			(3,571)
Issuance of common shares and deferred compensation amortization, net	440,835		4	440,831
Issuance of common shares and deferred compensation amortization, net (in shares)			40,947,537
Dividends/distributions	(148,076)				(144,206)		(3,870)
Net income	3,863				1,630		2,233
Other comprehensive income (loss)	10,663					10,663
Ending balance at Dec. 31, 2013	1,539,483	94,016	23	2,717,787	(1,300,527)	4,439	23,745
Ending balance (in shares) at Dec. 31, 2013		1,935,400	228,663,022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares	(1,962)			(858)			(1,104)
Redemption of noncontrolling OP units for common shares (in shares)			29,086
Issuance of common shares upon conversion of Convertible Notes	14,347			14,347
Issuance of common shares upon conversion of convertible notes (in shares)	1,904,542		1,904,542
Acquisition of consolidated joint venture partner's equity interest	(2,100)				(2,262)		162
Exercise of employee common share options, net	597			597
Exercise of employee common share options, net (in shares)			303,852
Forfeiture of employee common shares	(57)			(57)
Forfeiture of employee common shares (in shares)			(13,658)
Issuance of common shares and deferred compensation amortization, net	31,558			31,558
Issuance of common shares and deferred compensation amortization, net (in shares)			2,391,193
Dividends/distributions	(166,374)				(162,366)		(4,008)
Net income	97,463				93,104		4,359
Other comprehensive income (loss)	(4,035)					(4,035)
Ending balance at Dec. 31, 2014	$ 1,508,920	$ 94,016	$ 23	$ 2,763,374	$ (1,372,051)	$ 404	$ 23,154
Ending balance (in shares) at Dec. 31, 2014		1,935,400	233,278,037