Condensed Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance at Dec. 31, 2011	$ 758,363	$ 481	$ 170,483	$ 580,616	$ 6,783
Balance (in shares) at Dec. 31, 2011		48,163
Increase (Decrease) in Stockholders' Equity
Net income	23,060			23,060
Translation adjustment, net of tax	(2,725)				(2,725)
Stock options exercised	1,983	1	1,982
Stock options exercised (in shares)		82
Stock-based compensation	5,005		5,005
Tax effect of options exercised	(56)		(56)
Shares issued from release of Restricted Stock Units	(1,023)		(1,023)
Shares issued from release of Restricted Stock Units (in shares)		61
Cash dividends declared on common stock, $0.125, $0.375 and $0.25 per share for the period ended June 30, 2013, December 31, 2012 and June 30, 2012, respectively	(12,081)			(12,081)
Common stock issued at $33.81 and $33.71 per share for stock bonus for the period ended June 30, 2013 and June 30, 2012, respectively	418		418
Common stock issued (in shares)		12
Balance at Jun. 30, 2012	772,944	482	176,809	591,595	4,058
Balance (in shares) at Jun. 30, 2012		48,318
Increase (Decrease) in Stockholders' Equity
Net income	18,858			18,858
Translation adjustment, net of tax	8,284				8,284
Pension adjustment, net of tax	(243)				(243)
Stock options exercised	2,942	1	2,941
Stock options exercised (in shares)		103
Stock-based compensation	5,190		5,190
Tax effect of options exercised	(177)		(177)
Shares issued from release of Restricted Stock Units	(86)		(86)
Shares issued from release of Restricted Stock Units (in shares)		1
Cash dividends declared on common stock, $0.125, $0.375 and $0.25 per share for the period ended June 30, 2013, December 31, 2012 and June 30, 2012, respectively	(18,144)			(18,144)
Balance at Dec. 31, 2012	789,568	483	184,677	592,309	12,099
Balance (in shares) at Dec. 31, 2012		48,422
Increase (Decrease) in Stockholders' Equity
Net income	23,297			23,297
Translation adjustment, net of tax	(6,815)				(6,815)
Stock options exercised	776	1	775
Stock options exercised (in shares)		31
Stock-based compensation	5,649		5,649
Tax effect of options exercised	(1,850)		(1,850)
Shares issued from release of Restricted Stock Units	(2,019)	1	(2,020)
Shares issued from release of Restricted Stock Units (in shares)		107
Repurchase of common stock	(9,825)					(9,825)
Repurchase of common stock (in shares)		(342)
Cash dividends declared on common stock, $0.125, $0.375 and $0.25 per share for the period ended June 30, 2013, December 31, 2012 and June 30, 2012, respectively	(6,068)			(6,068)
Common stock issued at $33.81 and $33.71 per share for stock bonus for the period ended June 30, 2013 and June 30, 2012, respectively	318		318
Common stock issued (in shares)		9
Balance at Jun. 30, 2013	$ 793,031	$ 485	$ 187,549	$ 609,538	$ 5,284	$ (9,825)
Balance (in shares) at Jun. 30, 2013		48,227