Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance, value, beginning of period at Dec. 31, 2012	$ 839,903	$ 516,907	$ 284,440	$ 38,556
Balance, shares, beginning of period at Dec. 31, 2012		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	$ 0	$ 0
Repurchase of common stock, shares	0	0
Tax benefit of non-qualified stock option exercises and restricted stock unit vests, value	$ 6,424	$ 6,424
Conversion of convertible debt, shares		3,030,000
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)	0	0	(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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	105,064		105,064
Employee purchases of common stock through employee share purchase plan, value	9,862	$ 9,862
Employee purchases of common stock through employee share purchase plan, shares		139,000
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, value	4,736	$ 4,736
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, shares		433,000
Stock-based compensation expense, value	23,132	$ 23,132
Restricted stock unit taxes for net share settlement, value	(9,965)	$ (9,965)
Restricted stock unit taxes for net share settlement, shares		(116,000)
Repurchase of common stock, value	$ (62,523)	$ (62,523)
Repurchase of common stock, shares	(795,321)	(795,000)
Tax benefit of non-qualified stock option exercises and restricted stock unit vests, value	$ 4,526	$ 4,526
Translation adjustment, value	(71,406)			(71,406)
Unrealized gain (loss) on available for sale securities, value	(27)			(27)
Dividends declared on common stock, value	(36,436)		(36,436)
Minimum pension liability, net of taxes, value	(246)			(246)
Net adjustment for fair value of hedge derivatives, value	(2,960)	0	0	(2,960)
Balance, value, end of period at Dec. 31, 2014	$ 1,041,325	$ 607,250	461,586	(27,511)
Balance, shares, end of period at Dec. 31, 2014	41,797,000	41,797,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 124,009		124,009
Employee purchases of common stock through employee share purchase plan, value	9,540	$ 9,540
Employee purchases of common stock through employee share purchase plan, shares		139,000
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, value	6,301	$ 6,301
Restricted shares issued and stock options exercised related to employee stock-based compensation plans, shares		413,000
Stock-based compensation expense, value	22,379	$ 22,379
Restricted stock unit taxes for net share settlement, value	(7,301)	$ (7,301)
Restricted stock unit taxes for net share settlement, shares		(97,000)
Repurchase of common stock, value	$ (107,239)	$ (107,239)
Repurchase of common stock, shares	(1,396,693)	(1,397,000)
Tax benefit of non-qualified stock option exercises and restricted stock unit vests, value	$ 2,132	$ 2,132
Translation adjustment, value	(56,704)			(56,704)
Unrealized gain (loss) on available for sale securities, value	40			40
Dividends declared on common stock, value	(47,542)		(47,542)
Minimum pension liability, net of taxes, value	189			189
Net adjustment for fair value of hedge derivatives, value	2,947			2,947
Balance, value, end of period at Dec. 31, 2015	$ 990,076	$ 533,062	$ 538,053	$ (81,039)
Balance, shares, end of period at Dec. 31, 2015	40,855,000	40,855,000