Condensed Consolidated Statements of Equity (Unaudited) Statement - USD ($) $ 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	239		239
Common stock redemptions	(680)		(680)
Share-based compensation	2,822	1	2,821
Net income	9,180				9,180
Reclassification adjustments for losses included in net income (interest expense)	147			147
Gains (losses) arising during the period on interest rate swaps	513			513
Dividends to common stockholders ($0.30 per share)	(37,556)					(37,556)
Ending balance at Mar. 31, 2018	1,764,548	1,252	3,175,809	(639)	1,027,528	(2,439,402)
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]
Net income	46,908
Ending balance at Jun. 30, 2018	1,768,057	1,252	3,178,514	5	1,065,257	(2,476,971)
Beginning balance at Mar. 31, 2018	1,764,548	1,252	3,175,809	(639)	1,027,528	(2,439,402)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs	112		112
Share-based compensation	2,593	0	2,593
Net income	37,729				37,729
Reclassification adjustments for losses included in net income (interest expense)	127			127
Gains (losses) arising during the period on interest rate swaps	517			517
Dividends to common stockholders ($0.30 per share)	(37,569)					(37,569)
Ending balance at Jun. 30, 2018	1,768,057	1,252	3,178,514	5	1,065,257	(2,476,971)
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	120,500	38	120,462
Common stock redemptions	(570)		(570)
Share-based compensation	2,639	1	2,638
Net income	4,891				4,891
Reclassification adjustments for losses included in net income (interest expense)	15			15
Gains (losses) arising during the period on interest rate swaps	(724)			(724)
Dividends to common stockholders ($0.30 per share)	(37,614)					(37,614)
Ending balance at Mar. 31, 2019	1,805,779	1,292	3,302,814	(1,611)	1,093,010	(2,589,726)
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]
Net income	9,375
Ending balance at Jun. 30, 2019	1,769,444	1,292	3,305,344	(6,189)	1,097,494	(2,628,497)
Beginning balance at Mar. 31, 2019	1,805,779	1,292	3,302,814	(1,611)	1,093,010	(2,589,726)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs	159		159
Share-based compensation	2,371		2,371
Net income	4,484				4,484
Reclassification adjustments for losses included in net income (interest expense)	(1)			(1)
Gains (losses) arising during the period on interest rate swaps	(4,577)			(4,577)
Dividends to common stockholders ($0.30 per share)	(38,771)					(38,771)
Ending balance at Jun. 30, 2019	$ 1,769,444	$ 1,292	$ 3,305,344	$ (6,189)	$ 1,097,494	$ (2,628,497)