Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Net Income [Member]	Cumulative Dividends [Member]
Beginning Balance at Dec. 31, 2016	$ 1,653,414	$ 0	$ 1,164	$ 2,917,914	$ (1,401)	$ 995,256	$ (2,259,519)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	248,592		84	248,508
Common stock redemption	(3,018)		(1)	(3,017)
Share-based compensation	10,028		4	10,024
Net income	23,092					23,092
Gain on forward starting interest rate swaps	102				102
Dividends to common stockholders ($1.20 per share)	(142,327)						(142,327)
Ending Balance at Dec. 31, 2017	1,789,883	0	1,251	3,173,429	(1,299)	1,018,348	(2,401,846)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	616			616
Common stock redemption	(4,450)		(1)	(4,449)
Share-based compensation	10,691		3	10,688
Net income	69,771					69,771
Gain on forward starting interest rate swaps	397				397
Dividends to common stockholders ($1.20 per share)	(150,266)						(150,266)
Ending Balance at Dec. 31, 2018	1,716,642	0	1,253	3,180,284	(902)	1,088,119	(2,552,112)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	295,856		92	295,764
Common stock redemption	(3,318)		(1)	(3,317)
Share-based compensation	12,275		3	12,272
Net income	39,185					39,185
Loss on interest rate swaps	(5,273)				(5,273)
Dividends to common stockholders ($1.20 per share)	(155,358)						(155,358)
Ending Balance at Dec. 31, 2019	$ 1,900,009	$ 0	$ 1,347	$ 3,485,003	$ (6,175)	$ 1,127,304	$ (2,707,470)