Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance, value, beginning of period at Dec. 31, 2010	$ 633,174	$ 509,145	$ 75,024	$ 49,005
Balance, shares, beginning of period at Dec. 31, 2010		38,280,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	103,637		103,637
Employee purchases of common stock through employee share purchase plan, value	5,458	5,458
Employee purchases of common stock through employee share purchase plan, shares		212,000
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, value	18,854	18,854
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, shares		1,133,000
Stock-based compensation expense, value	11,111	11,111
Restricted stock unit taxes for net share settlement, value	(3,789)	(3,789)
Restricted stock unit taxes for net share settlement, shares		(105,000)
Repurchase of common stock, value	(50,000)	(50,000)
Repurchase of common stock, shares	(1,654,000)	(1,654,000)
Tax benefit of non-qualified stock option exercises and restricted stock unit vests, value	2,918	2,918
Conversion of convertible debt, value	1	1
Translation adjustment, value	(20,022)			(20,022)
Unrealized gain (loss) on available for sale securities, value	23			23
Minimum pension liability, net of taxes, value	0
Net adjustment for fair value of hedge derivatives, value	(4,551)			(4,551)
Balance, value, end of period at Dec. 31, 2011	696,814	493,698	178,661	24,455
Balance, shares, end of period at Dec. 31, 2011		37,866,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	114,920		114,920
Employee purchases of common stock through employee share purchase plan, value	7,007	7,007
Employee purchases of common stock through employee share purchase plan, shares		195,000
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, value	5,714	5,714
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, shares		551,000
Stock-based compensation expense, value	14,154	14,154
Restricted stock unit taxes for net share settlement, value	(5,913)	(5,913)
Restricted stock unit taxes for net share settlement, shares		(113,000)
Repurchase of common stock, value	(891)	(891)
Repurchase of common stock, shares	(20,500)	(21,000)
Tax benefit of non-qualified stock option exercises and restricted stock unit vests, value	3,137	3,137
Conversion of convertible debt, value	1	1
Translation adjustment, value	9,922			9,922
Unrealized gain (loss) on available for sale securities, value	(14)			(14)
Dividends declared on common stock, value	(9,141)		(9,141)
Minimum pension liability, net of taxes, value	(796)			(796)
Net adjustment for fair value of hedge derivatives, value	4,989	0	0	4,989
Balance, value, end of period at Dec. 31, 2012	839,903	516,907	284,440	38,556
Balance, shares, end of period at Dec. 31, 2012	38,478,000	38,478,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	126,673		126,673
Employee purchases of common stock through employee share purchase plan, value	8,618	8,618
Employee purchases of common stock through employee share purchase plan, shares		163,000
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, value	7,927	7,927
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, shares		574,000
Stock-based compensation expense, value	18,327	18,327
Restricted stock unit taxes for net share settlement, value	(9,658)	(9,658)
Restricted stock unit taxes for net share settlement, shares		(109,000)
Repurchase of common stock, value	(900)
Repurchase of common stock, shares	0
Tax benefit of non-qualified stock option exercises and restricted stock unit vests, value	6,424	6,424
Conversion of convertible debt, shares	3,000,000	3,030,000
Conversion of convertible debt, value	88,937	88,937
Translation adjustment, value	9,975			9,975
Unrealized gain (loss) on available for sale securities, value	(15)			(15)
Dividends declared on common stock, value	(18,155)		(18,155)
Minimum pension liability, net of taxes, value	267			267
Net adjustment for fair value of hedge derivatives, value	(1,655)			(1,655)
Balance, value, end of period at Dec. 31, 2013	$ 1,077,568	$ 637,482	$ 392,958	$ 47,128
Balance, shares, end of period at Dec. 31, 2013	42,136,000	42,136,000