Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income/(Loss)	Treasury Stock	Retained Earnings
Balance at Dec. 31, 2010	$ 883,886	$ 600	$ 928,690	$ (9,175)	$ (67,399)	$ 31,170
Balance (in shares) at Dec. 31, 2010		60,017,546
Increase (Decrease) in Stockholders' Equity
Net income	217,868					217,868
Foreign currency translation adjustments	(1,709)			(1,709)
Unrealized gain (loss) on available-for-sale securities	6			6
Defined benefit pension plan	(7)			(7)
Shares received upon sale of subsidiary	(2,750)				(2,750)
Conversion of 2011 convertible notes and exercise of convertible note hedge		7	27,287		(27,294)
Conversion of 2011 convertible notes and exercise of convertible note hedge (in shares)		650,827
Issuance of 2016 convertible notes	56,192		56,192
2016 convertible note hedge and warrants, net of tax	(29,069)		(29,069)
Repurchase of shares	(211,766)		(26,211)		(185,555)
Exercise of stock options	23,963	8	23,955
Exercise of stock options (in shares)	837,690	837,690
Tax benefit from exercises of non-qualified stock options	11,347		11,347
Share-based compensation	527		527
Balance at Dec. 31, 2011	948,488	615	992,718	(10,885)	(282,998)	249,038
Balance (in shares) at Dec. 31, 2011		61,506,063
Increase (Decrease) in Stockholders' Equity
Net income	304,442					304,442
Foreign currency translation adjustments	691			691
Unrealized gain (loss) on available-for-sale securities	67			67
Defined benefit pension plan	(4,830)			(4,830)
Repurchase of shares	(188,000)				(188,000)
Exercise of stock options	16,805	6	16,799
Exercise of stock options (in shares)	575,944	575,944
Tax benefit from exercises of non-qualified stock options	3,054		3,054
Share-based compensation	3,264		3,264
Balance at Dec. 31, 2012	1,083,981	621	1,015,835	(14,957)	(470,998)	553,480
Balance (in shares) at Dec. 31, 2012		62,082,007
Increase (Decrease) in Stockholders' Equity
Net income	174,560					174,560
Foreign currency translation adjustments	(1,193)			(1,193)
Unrealized gain (loss) on available-for-sale securities	(128)			(128)
Defined benefit pension plan	3,095			3,095
Shares issued under employee stock purchase plan	2,735	1	2,734
Shares issued under employee stock purchase plan (in shares)		55,070
Equity component -2016 convertible notes (Note 10)	(34,155)		(34,155)
Repurchase of shares	(42,439)				(42,439)
Exercise of stock options	26,619	8	26,611
Exercise of stock options (in shares)	876,115	876,115
Tax benefit from exercises of non-qualified stock options	9,299		9,299
Share-based compensation	36,900		36,900
Balance at Dec. 31, 2013	$ 1,259,274	$ 630	$ 1,057,224	$ (13,183)	$ (513,437)	$ 728,040
Balance (in shares) at Dec. 31, 2013		63,013,192