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, 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	0			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	107,133				104,975		2,158
Other comprehensive income	(5,581)					(5,581)
Ending Balance at Jun. 30, 2016	1,478,113	94,016	24	2,775,468	(1,406,774)	(7,520)	22,899
Beginning Balance at Dec. 31, 2016	1,412,491	94,016	24	2,800,736	(1,500,966)	(1,033)	19,714
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares	0			485			(485)
Issuance of common shares and deferred compensation amortization, net	20,996			20,996
Dividends/distributions	(88,423)				(86,668)		(1,755)
Net income	49,585				49,192		393
Other comprehensive income	1,476					1,476
Ending Balance at Jun. 30, 2017	$ 1,396,125	$ 94,016	$ 24	$ 2,822,217	$ (1,538,442)	$ 443	$ 17,867