Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	(Accumulated Deficit) Retained Earnings
BALANCE (in shares) at Dec. 31, 2014		116,764
BALANCE at Dec. 31, 2014	$ 1,481,500	$ 1,168	$ 1,748,303	$ (267,971)
Net income	173,256			173,256
Retirement of common stock (in shares)		(237)
Retirement of common stock	(9,454)	$ (3)	(9,451)
Dividends declared on common stock	(191,023)			(191,023)
Restricted stock compensation, net of forfeitures (in shares)		(9)
Restricted stock compensation, net of forfeitures	10,937		10,876	61
Income tax benefit of equity compensation	529		529
Stock option compensation expense, net of forfeitures	579		579
Restricted stock grants (in shares)		303
Restricted stock grants	3	$ 3
Stock options exercised (in shares)		402
Stock options exercised	7,554	$ 4	7,550
BALANCE (in shares) at Sep. 30, 2015		117,223
BALANCE at Sep. 30, 2015	1,473,881	$ 1,172	1,758,386	(285,677)
BALANCE (in shares) at Dec. 31, 2015		117,232
BALANCE at Dec. 31, 2015	1,462,748	$ 1,172	1,762,394	(300,818)
Net income	159,230			159,230
Retirement of common stock (in shares)		(135)
Retirement of common stock	(3,991)	$ (1)	(3,990)
Dividends declared on common stock	(191,956)			(191,956)
Restricted stock compensation, net of forfeitures (in shares)		(1)
Restricted stock compensation, net of forfeitures	13,925		13,868	57
Income tax benefit of equity compensation	1,492		1,492
Stock option compensation expense, net of forfeitures	104		104
Restricted stock grants (in shares)		314
Restricted stock grants	3	$ 3
Stock options exercised (in shares)		141
Stock options exercised	2,638	$ 2	2,636
BALANCE (in shares) at Sep. 30, 2016		117,551
BALANCE at Sep. 30, 2016	$ 1,444,193	$ 1,176	$ 1,776,504	$ (333,487)