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, 2013		115,923
BALANCE at Dec. 31, 2013	$ 1,502,507	$ 1,159	$ 1,725,363	$ (224,015)
Net income	195,022			195,022
Retirement of common stock (in shares)		(118)
Retirement of common stock	(4,036)	$ (1)	(4,035)
Dividends declared on common stock	(239,086)			(239,086)
Restricted stock compensation, net of forfeitures (in shares)		(20)
Restricted stock compensation, net of forfeitures	12,093		11,985	108
Stock option compensation expense, net of forfeitures	1,882		1,882
Income tax benefit of equity compensation	665		665
Restricted stock grants (in shares)		267
Restricted stock grants	3	$ 3
Stock options exercised (in shares)		712
Stock options exercised	12,450	$ 7	12,443
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	221,854			221,854
Retirement of common stock (in shares)		(237)
Retirement of common stock	(9,454)	$ (3)	(9,451)
Dividends declared on common stock	(254,774)			(254,774)
Restricted stock compensation, net of forfeitures (in shares)		(11)
Restricted stock compensation, net of forfeitures	14,712		14,639	73
Stock option compensation expense, net of forfeitures	682		682
Income tax benefit of equity compensation	525		525
Restricted stock grants (in shares)		303
Restricted stock grants	3	$ 3
Stock options exercised (in shares)		413
Stock options exercised	7,700	$ 4	7,696
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	219,919			219,919
Retirement of common stock (in shares)		(135)
Retirement of common stock	(4,006)	$ (1)	(4,005)
Dividends declared on common stock	(241,721)			(241,721)
Restricted stock compensation, net of forfeitures (in shares)		(1)
Restricted stock compensation, net of forfeitures	17,792		17,735	57
Stock option compensation expense, net of forfeitures	111		111
Income tax benefit of equity compensation	1,479		1,479
Restricted stock grants (in shares)		318
Restricted stock grants	3	$ 3
Stock options exercised (in shares)		140
Stock options exercised	2,638	$ 2	2,636
BALANCE (in shares) at Dec. 31, 2016		117,554
BALANCE at Dec. 31, 2016	$ 1,458,963	$ 1,176	$ 1,780,350	$ (322,563)