Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance at Dec. 31, 2015	$ 849,824	$ 481	$ 238,212	$ 639,707	$ (28,576)
Balance (in shares) at Dec. 31, 2015		48,184
Increase (Decrease) in Stockholders' Equity
Net income	42,544			42,544
Translation adjustment, net of tax	5,011				5,011
Options exercised	2,525	$ 1	2,524
Options exercised (in shares)		86
Stock-based compensation	5,951		5,951
Tax benefit of options exercised	19		19
Shares issued from release of Restricted Stock Units	(3,973)	$ 2	(3,975)
Shares issued from release of Restricted Stock Units (in shares)		215
Repurchase of common stock	(3,502)		0			$ (3,502)
Repurchase of common stock (in shares)		(106)
Cash dividends declared on common stock, $0.34, $0.36 and $0.39 for the period ended June 30, 2016, December 31, 2016 and June 30, 2017, respectively	(16,438)			(16,438)
Common stock issued at $32.45 per share for stock bonus for the periods ended June 30, 2016 and December 31, 2016 and $44.26 for the period ended June 30, 2017,	315		315
Common stock issued (in shares)		10
Balance at Jun. 30, 2016	882,276	$ 484	243,046	665,813	(23,565)	(3,502)
Balance (in shares) at Jun. 30, 2016		48,389
Balance at Dec. 31, 2015	849,824	$ 481	238,212	639,707	(28,576)
Balance (in shares) at Dec. 31, 2015		48,184
Increase (Decrease) in Stockholders' Equity
Net income	47,190			47,190
Translation adjustment, net of tax	(8,931)				(8,931)
Pension adjustment, net of tax	(474)				(474)
Options exercised	5,451	$ 2	5,449
Options exercised (in shares)		184
Stock-based compensation	7,235		7,235
Tax benefit of options exercised	232		232
Shares issued from release of Restricted Stock Units	(45)	$ 0	(45)
Shares issued from release of Restricted Stock Units (in shares)		2
Repurchase of common stock	(50,000)		0			(50,000)
Repurchase of common stock (in shares)		(1,138)
Retirement of common stock	0	$ (13)		(53,489)		53,502
Cash dividends declared on common stock, $0.34, $0.36 and $0.39 for the period ended June 30, 2016, December 31, 2016 and June 30, 2017, respectively	(17,092)			(17,092)
Balance at Dec. 31, 2016	865,842	$ 473	255,917	642,422	(32,970)
Balance (in shares) at Dec. 31, 2016		47,437
Increase (Decrease) in Stockholders' Equity
Net income	51,335			51,335
Translation adjustment, net of tax	13,949				13,949
Options exercised	1,297	$ 0	1,297
Options exercised (in shares)		44
Stock-based compensation	10,337		10,337
Tax benefit of options exercised	0
Shares issued from release of Restricted Stock Units	(5,155)	$ 2	(5,157)
Shares issued from release of Restricted Stock Units (in shares)		208
Repurchase of common stock	(20,000)		(2,456)			(17,544)
Repurchase of common stock (in shares)		(425)
Cash dividends declared on common stock, $0.34, $0.36 and $0.39 for the period ended June 30, 2016, December 31, 2016 and June 30, 2017, respectively	(18,606)			(18,606)
Common stock issued at $32.45 per share for stock bonus for the periods ended June 30, 2016 and December 31, 2016 and $44.26 for the period ended June 30, 2017,	412		412
Common stock issued (in shares)		9
Balance at Jun. 30, 2017	$ 899,411	$ 475	$ 260,350	$ 675,151	$ (19,021)	$ (17,544)
Balance (in shares) at Jun. 30, 2017		47,273