Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total Stockholders' Equity	Noncontrolling Interest
Balance, shares at Dec. 31, 2015		181,308
Balance, value at Dec. 31, 2015	$ 1,291,792	$ 1,813	$ 1,588,541	$ 22	$ (323,761)	$ 1,266,615	$ 25,177
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share repurchases, shares		(752)
Share repurchases, value	(7,280)	$ (7)	(7,273)			(7,280)
Dividend reinvestment plan (DRIP), shares		4,387
Dividend reinvestment plan (DRIP), value	44,731	$ 44	44,687			44,731
Common distributions declared, $0.50 per share	(92,107)				(92,107)	(92,107)
Share-based compensation, shares		0
Share-based compensation, value	10		10			10
Change in unrealized loss on interest rate swaps	(6,835)			(6,835)		(6,835)
Distributions to noncontrolling interests	(1,409)						(1,409)
Net income (loss)	5,326				5,243	5,243	83
Balance, shares at Sep. 30, 2016		184,943
Balance, value at Sep. 30, 2016	1,234,228	$ 1,850	1,625,965	(6,813)	(410,625)	1,210,377	23,851
Balance, shares at Dec. 31, 2016		185,062
Balance, value at Dec. 31, 2016	1,224,787	$ 1,851	1,627,098	10,587	(438,155)	1,201,381	23,406
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting pronouncement (see Note 8)				1,329	(1,329)	0
Balance at January 1, 2017, as adjusted at Jan. 01, 2017	1,224,787	$ 1,851	1,627,098	11,916	(439,484)	1,201,381	23,406
Balance, shares at Dec. 31, 2016		185,062
Balance, value at Dec. 31, 2016	1,224,787	$ 1,851	1,627,098	10,587	(438,155)	1,201,381	23,406
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share repurchases, shares		(4,471)
Share repurchases, value	(45,602)	$ (45)	(45,557)			(45,602)
Dividend reinvestment plan (DRIP), shares		3,546
Dividend reinvestment plan (DRIP), value	36,171	$ 35	36,136			36,171
Common distributions declared, $0.50 per share	(92,037)				(92,037)	(92,037)
Share-based compensation, shares		3
Share-based compensation, value	40		40			40
Change in unrealized loss on interest rate swaps	(741)			(741)		(741)
Distributions to noncontrolling interests	(1,384)						(1,384)
Redemption of noncontrolling Interest	(4,179)						(4,179)
Net income (loss)	(8,463)				(8,319)	(8,319)	(144)
Balance, shares at Sep. 30, 2017		184,140
Balance, value at Sep. 30, 2017	$ 1,108,592	$ 1,841	$ 1,617,717	$ 11,175	$ (539,840)	$ 1,090,893	$ 17,699