CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - 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, 2016	$ 1,412,491	$ 94,016	$ 24	$ 2,800,736	$ (1,500,966)	$ (1,033)	$ 19,714
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares and deferred compensation amortization, net	18,322		0	18,322
Dividends/distributions	(44,331)				(43,291)		(1,040)
Net income (loss)	42,220				42,040		180
Other comprehensive income	1,292					1,292
Ending Balance at Mar. 31, 2017	1,429,994	94,016	24	2,819,058	(1,502,217)	259	18,854
Beginning Balance at Dec. 31, 2017	1,340,835	94,016	24	2,818,520	(1,589,724)	1,065	16,934
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares and deferred compensation amortization, net	1,660			1,660
Repurchase of common shares	(6,336)			(6,336)
Repurchase of common shares to settle tax obligations	(2,544)			(2,544)
Forfeiture of employee common shares	(78)			(87)	9
Dividends/distributions	(44,576)				(43,774)		(802)
Net income (loss)	(14,823)				(14,315)		(508)
Other comprehensive income	246					246
Ending Balance at Mar. 31, 2018	$ 1,274,384	$ 94,016	$ 24	$ 2,811,213	$ (1,647,804)	$ 1,311	$ 15,624