Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member] Class A [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Total	Class A [Member]
Balance at beginning 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)	$ (140,865)
Exercise of employee stock options/vesting of stock awards	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
Stockholders' equity [Roll Forward]
Net income	0	0	0	0	189,176	189,176
Other comprehensive income, net of tax	0	0	0	(5,293)	0	(5,293)
Repurchase of Class A common stock (Note 11)	0	0	(45,724)	0	0	(45,724)	(45,724)
Exercise of employee stock options/vesting of stock awards	0	(12,440)	10,020	0	0	(2,420)
Excess tax benefit from equity awards	0	11,947	0	0	0	11,947
Stock-based compensation	0	17,504	0	0	0	17,504
Cash dividends	0	0	0	0	(81,371)	(81,371)
Balance at end of period at Dec. 31, 2014	91	414,394	(862,608)	(51,521)	1,442,082	942,438
Stockholders' equity [Roll Forward]
Net income	0	0	0	0	133,046	133,046
Other comprehensive income, net of tax	0	0	0	(19,748)	0	(19,748)
Repurchase of Class A common stock (Note 11)	0	0	(164,094)	0	0	(164,094)	$ (164,100)
Exercise of employee stock options/vesting of stock awards	0	(6,324)	9,639	0	0	3,315
Excess tax benefit from equity awards	0	4,451	0	0	0	4,451
Stock-based compensation	0	7,400	0	0	0	7,400
Cash dividends	0	0	0	0	(81,187)	(81,187)
Balance at end of period at Dec. 31, 2015	$ 91	$ 419,921	$ (1,017,063)	$ (71,269)	$ 1,493,941	$ 825,621