Consolidated Statements of Equity - USD ($) $ in Thousands	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Cumulative Net Income	Cumulative Dividends	Total Stockholders' Equity
Beginning Balance at Dec. 31, 2015	$ 0	$ 1,015	$ 2,461,376	$ (1,569)	$ 909,685	$ (2,127,760)	$ 1,242,747
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs		140	450,409				450,549
Common stock redemption			(1,460)				(1,460)
Stock-based compensation		9	7,589				7,598
Net income					85,571		85,571
Loss on interest rate swaps				168			168
Dividends to common stockholders ($1.20 per share)						(131,759)	(131,759)
Ending Balance at Dec. 31, 2016	0	1,164	2,917,914	(1,401)	995,256	(2,259,519)	1,653,414
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs		84	248,508				248,592
Common stock redemption		(1)	(3,017)				(3,018)
Stock-based compensation		4	10,024				10,028
Net income					23,092		23,092
Loss on interest rate swaps				102			102
Dividends to common stockholders ($1.20 per share)						(142,327)	(142,327)
Ending Balance at Dec. 31, 2017	0	1,251	3,173,429	(1,299)	1,018,348	(2,401,846)	1,789,883
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs			616				616
Common stock redemption		(1)	(4,449)				(4,450)
Stock-based compensation		3	10,688				10,691
Net income					69,771		69,771
Loss on interest rate swaps				397			397
Dividends to common stockholders ($1.20 per share)						(150,266)	(150,266)
Ending Balance at Dec. 31, 2018	$ 0	$ 1,253	$ 3,180,284	$ (902)	$ 1,088,119	$ (2,552,112)	$ 1,716,642