Consolidated Statements of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Loss on Pension Benefit Obligation	Currency Translation Adjustments	Foreign Currency Hedge Adjustment	Commodity Hedge Adjustment	Accumulated Earnings
Beginning Balance at Dec. 31, 2014	$ 294,219	$ 243,255	$ (8,224)	$ (2,673)	$ (23,060)	$ (10)		$ 84,931
Beginning Balance (in shares) at Dec. 31, 2014		35,697,000
Exercise of Common Stock options for cash	$ 9,273	$ 12,146	(2,873)
Exercise of Common Stock options for cash (in shares)	571,723	571,000
Tax benefit from Exercises of Common Stock options	$ 6,681		6,681
Common Stock issued to Board of Directors and employees	3,734	$ 3,734
Common Stock issued to Board of Directors and employees (in shares)		108,000
Stock option compensation	3,025		3,025
Cancelation of restricted stock	(2,216)	$ (2,216)
Cancelation of restricted stock (in shares)		(54,000)
Net gain (loss) on pension benefit obligation, net	613			613
Currency translation, net	(26,212)		109		(26,321)
Foreign currency hedge, net	10					10
Commodity hedge, net	(229)						$ (229)
Net income	95,393							95,393
Ending Balance at Dec. 31, 2015	384,291	$ 256,919	(1,282)	(2,060)	(49,381)		(229)	180,324
Ending Balance (in shares) at Dec. 31, 2015		36,322,000
Exercise of Common Stock options for cash	$ 1,438	$ 1,939	(501)
Exercise of Common Stock options for cash (in shares)	112,875	113,000
Tax benefit from Exercises of Common Stock options	$ 7,509		7,509
Common Stock issued to Board of Directors and employees	4,589	$ 4,589
Common Stock issued to Board of Directors and employees (in shares)		137,000
Stock option compensation	4,597		4,597
Cancelation of restricted stock	(1,196)	$ (1,196)
Cancelation of restricted stock (in shares)		(38,000)
Net gain (loss) on pension benefit obligation, net	(490)			(490)
Currency translation, net	(16,381)				(16,381)
Foreign currency hedge, net	(1,020)					(1,020)
Commodity hedge, net	470						470
Net income	76,598							76,598
Ending Balance at Dec. 31, 2016	$ 460,405	$ 262,251	10,323	(2,550)	(65,762)	(1,020)	241	256,922
Ending Balance (in shares) at Dec. 31, 2016	36,534,464	36,534,000
Exercise of Common Stock options for cash	$ 2,755	$ 3,662	(907)
Exercise of Common Stock options for cash (in shares)	202,328	202,000
Cumulative effect of accounting change due to adoption of ASU 2016-09	$ 1,496							1,496
Common Stock issued to Board of Directors and employees	6,298	$ 6,298
Common Stock issued to Board of Directors and employees (in shares)		242,000
Stock repurchase	(5,326)	$ (5,326)
Stock repurchase (in shares)		(164,000)
Stock option compensation	6,209		6,209
Cancelation of restricted stock	(1,837)	$ (1,837)
Cancelation of restricted stock (in shares)		(53,000)
Net gain (loss) on pension benefit obligation, net	184			184
Currency translation, net	48,207				48,207
Foreign currency hedge, net	220					220
Commodity hedge, net	36						36
Net income	35,227							35,227
Ending Balance at Dec. 31, 2017	$ 553,874	$ 265,048	$ 15,625	$ (2,366)	$ (17,555)	$ (800)	$ 277	$ 293,645
Ending Balance (in shares) at Dec. 31, 2017	36,761,362	36,761,000