Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Common Stock Dividends in excess of Earnings	Accumulated Other Comprehensive Income (Loss)	Total Stockholders' Equity	Noncontrolling Interest - Unit holders in Operating Partnership	Series C Preferred Stock
Balance at Dec. 31, 2015	$ 857,857	$ 139,000	$ 681	$ 1,017,397	$ (332,271)	$ (2,350)	$ 822,457	$ 35,400
Balance (in shares) at Dec. 31, 2015			68,077,333
Increase (Decrease) in Stockholders' Equity
Proceeds from sale of stock		75,000
Offering costs	(2,655)			(2,655)			(2,655)
Issuance of restricted stock, net	1
Dividends and distributions, net	$ (57,450)	(6,913)			(47,386)		(54,299)	(3,151)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	109,042
Non-cash compensation activity	$ 5,686			1,797			1,798	3,888
Rebalancing of noncontrolling interest				1,564			1,564	(1,564)
Other comprehensive loss	(16,891)					(16,023)	(16,023)	(868)
Net income (loss)	2,391	6,913			(4,290)		2,623	(232)
Balance at Jun. 30, 2016	863,938	214,000	$ 682	1,018,103	(383,947)	(18,373)	830,465	33,473
Balance (in shares) at Jun. 30, 2016			68,186,375
Balance at Dec. 31, 2015	857,857	139,000	$ 681	1,017,397	(332,271)	(2,350)	822,457	35,400
Balance (in shares) at Dec. 31, 2015			68,077,333
Balance at Dec. 31, 2016	1,066,926	145,000	$ 804	1,293,706	(410,978)	(1,496)	1,027,036	39,890
Balance (in shares) at Dec. 31, 2016			80,352,304
Increase (Decrease) in Stockholders' Equity
Proceeds from sale of stock	274,385		$ 107	274,278			274,385
Proceeds from sales of common stock (in shares)			10,756,543						3,000,000
Offering costs	(3,899)			(3,899)			(3,899)
Dividends and distributions, net	$ (68,811)	(4,897)			(60,269)		(65,166)	(3,645)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	40,301
Non-cash compensation activity	$ 3,832			1,684			1,490	2,342
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures					(194)
Issuance of units	18,558							18,558
Rebalancing of noncontrolling interest				3,907			3,907	(3,907)
Other comprehensive loss	(298)					(285)	(285)	(13)
Net income (loss)	1,437	4,897			(3,315)		1,582	(145)
Balance at Jun. 30, 2017	$ 1,292,130	$ 145,000	$ 914	1,572,943	$ (474,756)	$ (1,781)	1,242,320	49,810
Balance (in shares) at Jun. 30, 2017			91,446,154.000
Increase (Decrease) in Stockholders' Equity
Stock Issued During Period, Value, Conversion of Units			$ 3	$ 3,267			$ 3,270	$ (3,270)
Stock Issued During Period, Shares, Conversion of Units			297,006