Consolidated Statement of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2015	$ 1,462,748	$ 1,172	$ 1,762,394	$ (300,818)
Balance (in shares) at Dec. 31, 2015		117,232
Net income	103,890			103,890
Retirement of common stock	(3,947)	$ (1)	(3,946)
Retirement of common stock (in shares)		(134)
Dividends declared on common stock	(127,998)			(127,998)
Restricted stock compensation, net of forfeitures	7,777		7,720	57
Restricted stock compensation, net of forfeitures (in shares)		(1)
Income tax benefit of equity compensation	25		25
Stock option compensation expense, net of forfeitures	96		96
Restricted stock grants	3	$ 3
Restricted stock grants (in shares)		310
Stock options exercised	2,033	$ 1	2,032
Stock options exercised (in shares)		113
Balance at Jun. 30, 2016	1,444,627	$ 1,175	1,768,321	(324,869)
Balance (in shares) at Jun. 30, 2016		117,520
Balance at Dec. 31, 2016	1,458,963	$ 1,176	1,780,350	(322,563)
Balance (in shares) at Dec. 31, 2016		117,554
Net income	95,522			95,522
Retirement of common stock	(5,818)	$ (2)	(5,816)
Retirement of common stock (in shares)		(175)
Dividends declared on common stock	(100,134)			(100,134)
Restricted stock compensation, net of forfeitures	8,145		8,145
Restricted stock grants		$ 5	(5)
Restricted stock grants (in shares)		507
Stock options exercised	6,666	$ 3	6,663
Stock options exercised (in shares)		293
Balance at Jun. 30, 2017	$ 1,463,344	$ 1,182	$ 1,789,337	$ (327,175)
Balance (in shares) at Jun. 30, 2017		118,179