Condensed Consolidated Statements of Equity (Unaudited) Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Cumulative Net Income	Cumulative Dividends
Beginning balance at Dec. 31, 2017	$ 1,789,883	$ 1,251	$ 3,173,429	$ (1,299)	$ 1,018,348	$ (2,401,846)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs	464		464
Common stock redemptions	(719)		(719)
Share-based compensation	8,090	1	8,089
Net income	53,456				53,456
Reclassification adjustments for losses included in net income (interest expense)	369			369
Losses arising during the period on interest rate swaps	1,403			1,403
Dividends to common stockholders	(112,694)					(112,694)
Ending balance at Sep. 30, 2018	1,740,252	1,252	3,181,263	473	1,071,804	(2,514,540)
Beginning balance at Jun. 30, 2018	1,768,055	1,252	3,178,514	4	1,065,256	(2,476,971)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs	113		113
Common stock redemptions	(39)		(39)
Share-based compensation	2,675	0	2,675
Net income	6,548				6,548
Reclassification adjustments for losses included in net income (interest expense)	95			95
Losses arising during the period on interest rate swaps	374			374
Dividends to common stockholders	(37,569)					(37,569)
Ending balance at Sep. 30, 2018	1,740,252	1,252	3,181,263	473	1,071,804	(2,514,540)
Beginning balance at Dec. 31, 2018	1,716,642	1,253	3,180,284	(902)	1,088,119	(2,552,112)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs	192,475	$ 61	192,414
Stock Repurchased and Retired During Period, Shares		(1)
Common stock redemptions	(3,267)		(3,266)
Share-based compensation	10,141	$ 1	10,140
Net income	11,975				11,975
Reclassification adjustments for losses included in net income (interest expense)	74			74
Losses arising during the period on interest rate swaps	(7,642)			(7,642)
Dividends to common stockholders	(115,237)					(115,237)
Ending balance at Sep. 30, 2019	1,805,161	1,314	3,379,572	(8,470)	1,100,094	(2,667,349)
Beginning balance at Jun. 30, 2019	1,769,443	1,292	3,305,344	(6,189)	1,097,493	(2,628,497)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs	71,814	22	71,792
Common stock redemptions	(2,695)		(2,695)
Share-based compensation	5,131		5,131
Net income	2,601				2,601
Reclassification adjustments for losses included in net income (interest expense)	60			60
Losses arising during the period on interest rate swaps	(2,341)			(2,341)
Dividends to common stockholders	(38,852)					(38,852)
Ending balance at Sep. 30, 2019	$ 1,805,161	$ 1,314	$ 3,379,572	$ (8,470)	$ 1,100,094	$ (2,667,349)