CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Preferred Shares [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, 2013	$ 1,539,483	$ 94,016	$ 23	$ 2,717,787	$ (1,300,527)	$ 4,439	$ 23,745
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares upon conversion of convertible notes	4,834			4,834
Redemption of noncontrolling OP units	(1,962)			(950)			(1,012)
Issuance of common shares and deferred compensation amortization, net	25,594			25,594
Acquisition of consolidated joint venture partner's equity interest	(2,100)				(2,262)		162
Dividends/distributions	(124,018)				(121,137)		(2,881)
Net income (loss)	59,278				55,741		3,537
Other comprehensive loss	(1,134)					(1,134)
Ending Balance at Sep. 30, 2014	1,499,975	94,016	23	2,747,265	(1,368,185)	3,305	23,551
Beginning Balance at Dec. 31, 2014	1,508,920	94,016	23	2,763,374	(1,372,051)	404	23,154
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares upon conversion of convertible notes	3,630			3,630
Repurchase of common shares	(11,019)			(11,019)
Issuance of common shares and deferred compensation amortization, net	23,852		1	23,851
Acquisition of consolidated joint venture partner's equity interest	(1,234)				(1,247)		13
Dividends/distributions	(128,837)				(125,972)		(2,865)
Net income (loss)	79,378				76,853		2,525
Other comprehensive loss	(6,620)					(6,620)
Ending Balance at Sep. 30, 2015	$ 1,468,070	$ 94,016	$ 24	$ 2,779,836	$ (1,422,417)	$ (6,216)	$ 22,827