Consolidated Statements of Shareholders' Equity - 3 months ended Mar. 31, 2016 - USD ($) shares in Thousands, $ in Thousands	Total	Shares of Beneficial Interest at Par Value [Member]	Additional Paid in Capital [Member]	Distributions in Excess of Net Income Attributable to the Controlling Interests [Member]	AOCI Attributable to Parent [Member]	Total Shareholders' Equity [Member]	Noncontrolling Interests in Subsidiaries [Member]
Balance (in shares) at Dec. 31, 2015		68,191
Balance at Dec. 31, 2015	$ 837,012	$ 682	$ 1,193,298	$ (357,781)	$ (550)	$ 835,649	$ 1,363
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to the controlling interests	2,384			2,384		2,384
Less: Net loss attributable to noncontrolling interests	(5)						(5)
Other Comprehensive Income (Loss), Net of Tax	(3,675)				(3,675)	(3,675)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(91)						(91)
Dividends	(20,644)			(20,644)		(20,644)
Share grants, net of share grant amortization and forfeitures (in shares)		135
Share grants, net of share grant amortization and forfeitures	453	$ 1	452			453
Balance at Mar. 31, 2016	$ 815,434	$ 683	$ 1,193,750	$ (376,041)	$ (4,225)	$ 814,167	$ 1,267
Balance (in shares) at Mar. 31, 2016		68,326