CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	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, 2012	$ 1,333,165	$ 243,790	$ 18	$ 2,212,949	$ (1,143,803)	$ (6,224)	$ 26,435
Beginning 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
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
Acquisition of consolidated joint venture partner's equity interest	(8,918)				(8,918)
Exercise of employee common share options	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)
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
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
Acquisition of consolidated joint venture partner's equity interest	(2,100)				(2,262)		162
Exercise of employee common share options	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)
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares				165			(165)
Redemption of noncontrolling OP units for common shares (in shares)			32,780
Repurchase of common shares	(18,431)			(18,431)
Repurchase of common shares (in shares)			(2,216,799)
Issuance of common shares upon conversion of convertible notes	$ 3,630			3,630
Issuance of common shares upon conversion of Convertible Notes (in shares)	519,664		519,664
Issuance of common shares and deferred compensation amortization, net	$ 28,099			28,099
Issuance of common shares and deferred compensation amortization, net (in shares)			2,961,543
Acquisition of consolidated joint venture partner's equity interest	(1,234)				(1,247)		13
Dividends/distributions	(171,001)				(167,313)		3,688
Net income	114,891				111,703		3,188
Other comprehensive income (loss)	(2,343)					(2,343)
Ending balance at Dec. 31, 2015	$ 1,462,531	$ 94,016	$ 23	$ 2,776,837	$ (1,428,908)	$ (1,939)	$ 22,502
Ending balance (in shares) at Dec. 31, 2015		1,935,400	234,575,225