CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY (USD $) In Thousands	Total	Class A Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2010	$ 730,032	$ 722	$ 129,715	$ (462,029)	$ 1,070,973	$ (9,349)
Repurchase of Class A Common Stock	(160,200)			(160,200)
Issuance of treasury shares upon exercise of stock options, purchases under stock purchase plan and grants of restricted stock awards	13,009		(12,598)	25,607
Additional tax benefit resulting from exercise of options	210		210
Equity-based compensation	14,095		14,095
Net income	174,643				174,643
Unrealized holding gain (loss) on investments, net of income taxes	(385)					(385)
Unrealized gain (loss) on hedging transactions, net of income taxes	6,209					6,209
Foreign currency translation adjustment	(688)					(688)
Ending Balance at Dec. 31, 2011	776,925	722	131,422	(596,622)	1,245,616	(4,213)
Repurchase of Class A Common Stock	(54,373)			(54,373)
Issuance of treasury shares upon exercise of stock options, purchases under stock purchase plan and grants of restricted stock awards	3,361		(6,196)	9,557
Additional tax benefit resulting from exercise of options	(430)		(430)
Equity-based compensation	14,727		14,727
Net income	122,904				122,904
Unrealized holding gain (loss) on investments, net of income taxes	887					887
Unrealized gain (loss) on hedging transactions, net of income taxes	(7,241)					(7,241)
Foreign currency translation adjustment	242					242
Ending Balance at Dec. 31, 2012	857,002	722	139,523	(641,438)	1,368,520	(10,325)
Repurchase of Class A Common Stock	(63,102)			(63,102)
Issuance of treasury shares upon exercise of stock options, purchases under stock purchase plan and grants of restricted stock awards	14,652		(11,432)	26,084
Additional tax benefit resulting from exercise of options	2,095		2,095
Equity-based compensation	13,109		13,109
Net income	134,358				134,358
Unrealized holding gain (loss) on investments, net of income taxes	(456)					(456)
Unrealized gain (loss) on hedging transactions, net of income taxes	118					118
Foreign currency translation adjustment	882					882
Ending Balance at Dec. 31, 2013	$ 958,658	$ 722	$ 143,295	$ (678,456)	$ 1,502,878	$ (9,781)