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	159,230			159,230
Retirement of common stock	(3,991)	$ (1)	(3,990)
Retirement of common stock (in shares)		(135)
Dividends declared on common stock	(191,956)			(191,956)
Restricted stock compensation, net of forfeitures	13,925		13,868	57
Restricted stock compensation, net of forfeitures (in shares)		(1)
Income tax benefit of equity compensation	1,492		1,492
Stock option compensation expense, net of forfeitures	104		104
Restricted stock grants	3	$ 3
Restricted stock grants (in shares)		314
Stock options exercised	2,638	$ 2	2,636
Stock options exercised (in shares)		141
Balance at Sep. 30, 2016	1,444,193	$ 1,176	1,776,504	(333,487)
Balance (in shares) at Sep. 30, 2016		117,551
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	136,700			136,700
Retirement of common stock	(5,818)	$ (2)	(5,816)
Retirement of common stock (in shares)		(175)
Dividends declared on common stock	(150,206)			(150,206)
Restricted stock compensation, net of forfeitures	12,203		12,203
Restricted stock grants		$ 5	(5)
Restricted stock grants (in shares)		509
Stock options exercised	6,839	$ 3	6,836
Stock options exercised (in shares)		303
Balance at Sep. 30, 2017	$ 1,458,681	$ 1,182	$ 1,793,568	$ (336,069)
Balance (in shares) at Sep. 30, 2017		118,191