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, 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	3,733			3,733
Issuance of common shares and deferred compensation amortization, net	17,317		1	17,316
Dividends/distributions	(84,827)				(82,956)		(1,871)
Net income	84,578				82,837		1,741
Other comprehensive loss	(2,630)					(2,630)
Ending Balance at Jun. 30, 2015	1,527,091	94,016	24	2,784,423	(1,372,170)	(2,226)	23,024
Beginning Balance at Dec. 31, 2015	1,462,531	94,016	23	2,776,837	(1,428,908)	(1,939)	22,502
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common shares	(8,973)			(8,973)
Redemption of noncontrolling OP units for common shares				22			(22)
Issuance of common shares and deferred compensation amortization, net	7,583		1	7,582
Dividends/distributions	(84,580)				(82,841)		(1,739)
Net income	100,137				98,245		1,892
Other comprehensive loss	(5,581)					(5,581)
Ending Balance at Jun. 30, 2016	$ 1,471,117	$ 94,016	$ 24	$ 2,775,468	$ (1,413,504)	$ (7,520)	$ 22,633