Consolidated Statements of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Retained Earnings (Accumulated Deficit)
Balance, at Dec. 31, 2010	$ 1,122,188	$ 22,755	$ 1,269,525	$ 2,469	$ (172,561)
Balance, Shares at Dec. 31, 2010		182,035
Issuance of stock to employees under benefit plans, net of shares withheld for payroll tax (in shares)		4,185
Issuance of stock to employees under benefit plans, net of shares withheld for payroll tax	5,088	522	4,566
Stock-based compensation expense	32,337		32,337
Repurchase of common stock, shares		(2,633)
Repurchase of common stock	(31,175)	(329)	(17,770)		(13,076)
Stock options issued in purchase acquisition	4,472		4,472
Net income	369,873				369,873
Unrealized gain on marketable securities
Unrealized gain on marketable securities, net of tax of $216 in 2013, $370 in 2012 and $1,247 in 2011	1,409			1,409
Less: reclassification adjustment for gains included in net income, net of tax of $(257) in 2013, $(201) in 2012 and $(581) in 2011	(1,412)			(1,412)
Foreign currency translation adjustment	2,266			2,266
Amortization of prior service costs, net of tax of $(159) in 2013, $(134) in 2012 and $9 in 2011	14			14
Balance, at Dec. 31, 2011	1,505,060	22,948	1,293,130	4,746	184,236
Balance, Shares at Dec. 31, 2011		183,587
Issuance of stock to employees under benefit plans, net of shares withheld for payroll tax (in shares)		4,321
Issuance of stock to employees under benefit plans, net of shares withheld for payroll tax	6,894	540	6,354
Stock-based compensation expense	39,920		39,920
Repurchase of common stock, shares	0
Tax benefit related to stock options and restricted stock units	8,358		8,358
Net income	217,049				217,049
Unrealized gain on marketable securities
Unrealized gain on marketable securities, net of tax of $216 in 2013, $370 in 2012 and $1,247 in 2011	2,009			2,009
Less: reclassification adjustment for gains included in net income, net of tax of $(257) in 2013, $(201) in 2012 and $(581) in 2011	(702)			(702)
Amortization of prior service costs, net of tax of $(159) in 2013, $(134) in 2012 and $9 in 2011	(233)			(233)
Balance, at Dec. 31, 2012	1,778,355	23,488	1,347,762	5,820	401,285
Balance, Shares at Dec. 31, 2012		187,908
Issuance of stock to employees under benefit plans, net of shares withheld for payroll tax (in shares)		3,823
Issuance of stock to employees under benefit plans, net of shares withheld for payroll tax	5,404	478	4,926
Stock-based compensation expense	35,612		35,612
Repurchase of common stock, shares	0
Tax benefit related to stock options and restricted stock units	2,596		2,596
Net income	164,947				164,947
Unrealized gain on marketable securities
Unrealized gain on marketable securities, net of tax of $216 in 2013, $370 in 2012 and $1,247 in 2011	(1,097)			(1,097)
Less: reclassification adjustment for gains included in net income, net of tax of $(257) in 2013, $(201) in 2012 and $(581) in 2011	(447)			(447)
Amortization of prior service costs, net of tax of $(159) in 2013, $(134) in 2012 and $9 in 2011	(276)			(276)
Balance, at Dec. 31, 2013	$ 1,985,094	$ 23,966	$ 1,390,896	$ 4,000	$ 566,232
Balance, Shares at Dec. 31, 2013		191,731