Consolidated Statements of Stockholder's Equity and Comprehensive Income (USD $) In Thousands, unless otherwise specified	Common Class A [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balance at beginning of period at Dec. 31, 2010	$ 91	$ 256,505	$ (476,748)	$ (58,539)	$ 749,940	$ 471,249
Stockholders' equity [Roll Forward]
Net income	0	0	0	0	153,330	153,330
Other comprehensive income, net of tax	0	0	0	(4,026)	0	(4,026)
Repurchase of Class A common stock (Note 11)	0	0	(67,149)	0	0	(67,149)
Exercise of employee stock options	0	7,978	21,735	0	0	29,713
Excess tax benefit from equity awards	0	12,657	0	0	0	12,657
Stock-based compensation	0	15,100	0	0	0	15,100
Cash dividends	0	0	0	0	(36,638)	(36,638)
Balance at end of period at Dec. 31, 2011	91	292,240	(522,162)	(62,565)	866,632	574,236
Stockholders' equity [Roll Forward]
Net income	0	0	0	0	221,645	221,645
Other comprehensive income, net of tax	0	0	0	10,743	0	10,743
Repurchase of Class A common stock (Note 11)	0	0	(201,471)	0	0	(201,471)
Exercise of employee stock options	0	(4,214)	8,780	0	0	4,566
Excess tax benefit from equity awards	0	7,909	0	0	0	7,909
Stock-based compensation	0	21,358	0	0	0	21,358
Cash dividends	0	0	0	0	(48,374)	(48,374)
Balance at end of period at Dec. 31, 2012	91	317,293	(714,853)	(51,822)	1,039,903	590,612
Stockholders' equity [Roll Forward]
Net income	0	0	0	0	364,888	364,888
Other comprehensive income, net of tax	0	0	0	5,594	0	5,594
Repurchase of Class A common stock (Note 11)	0	0	(140,865)	0	0	(140,865)
Exercise of employee stock options	0	5,556	28,814	0	0	34,370
Excess tax benefit from equity awards	0	41,914	0	0	0	41,914
Stock-based compensation	0	32,620	0	0	0	32,620
Cash dividends	0	0	0	0	(70,514)	(70,514)
Balance at end of period at Dec. 31, 2013	$ 91	$ 397,383	$ (826,904)	$ (46,228)	$ 1,334,277	$ 858,619