Revenue from Contracts with Customers - Impact on Consolidated Income Statement and Consolidated Balance Sheet (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Assets:
Contract assets	$ 19,125	$ 24,756		$ 24,756		$ 0
Inventories	65,155	91,879		91,879		80,339
Liabilities:
Accounts payable	72,594	88,195		88,195		71,931
Other accrued liabilities	12,899	14,507		14,507		11,690
Deferred tax liabilities	15,185	41,064		41,064		14,714
Stockholders' equity:
Retained earnings	376,381	404,141		404,141		374,783
Accumulated other comprehensive loss		(28,726)		(28,726)		(20,148)
Income Statement
Net sales		197,886	$ 180,041	575,959	$ 520,407
Cost of sales		162,747	139,987	465,186	396,528
Gross profit		35,139	40,054	110,773	123,879
Selling, product development and administrative expenses		25,406	24,700	74,755	73,339
Operating income		9,733	15,354	36,018	50,540
Interest expense		1,505	705	2,617	2,106
Other income, net		(40)	601	(93)	1,727
Income before income taxes		8,268	14,048	33,494	46,707
Income tax expense		2,076	3,404	5,854	11,201
Income from equity method investment		(64)	(31)	(120)	37
Net income		$ 6,256	$ 10,675	$ 27,760	$ 35,469
Earnings per share:
Basic (USD per share)		$ 0.36	$ 0.63	$ 1.61	$ 2.08
Diluted (USD per share)		$ 0.36	$ 0.62	$ 1.60	$ 2.05
Weighted average number of common shares outstanding:
Basic average common shares outstanding		17,216	17,055	17,189	17,028
Diluted average common shares outstanding		17,349	17,267	17,339	17,270
Calculated under Revenue Guidance in Effect before Topic 606
Assets:
Contract assets		$ 0		$ 0		0
Inventories		113,718		113,718		80,339
Liabilities:
Accounts payable		86,502		86,502		71,931
Other accrued liabilities		16,655		16,655		11,690
Deferred tax liabilities		40,306		40,306		14,714
Stockholders' equity:
Retained earnings		401,489		401,489		$ 374,783
Accumulated other comprehensive loss		(28,688)		(28,688)
Income Statement
Net sales		198,949		569,160
Cost of sales		164,793		459,728
Gross profit		34,156		109,432
Selling, product development and administrative expenses		25,406		74,755
Operating income		8,750		34,677
Interest expense		1,505		2,617
Other income, net		(40)		(93)
Income before income taxes		7,285		32,153
Income tax expense		1,846		5,567
Income from equity method investment		(64)		(120)
Net income		$ 5,503		$ 26,706
Earnings per share:
Basic (USD per share)		$ 0.32		$ 1.55
Diluted (USD per share)		$ 0.32		$ 1.54
Weighted average number of common shares outstanding:
Basic average common shares outstanding		17,216		17,189
Diluted average common shares outstanding		17,349		17,339
Accounting Standards Update 2014-09
Assets:
Contract assets	5,631
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Assets:
Contract assets	19,125	$ 24,756		$ 24,756
Inventories	(15,184)	(21,839)		(21,839)
Liabilities:
Accounts payable	663	1,693		1,693
Other accrued liabilities	1,209	(2,148)		(2,148)
Deferred tax liabilities	471	758		758
Stockholders' equity:
Retained earnings	1,598	2,652		2,652
Accumulated other comprehensive loss		(38)		(38)
Income Statement
Net sales	$ 19,600	(1,063)		6,799
Cost of sales		(2,046)		5,458
Gross profit		983		1,341
Selling, product development and administrative expenses		0		0
Operating income		983		1,341
Interest expense		0		0
Other income, net		0		0
Income before income taxes		983		1,341
Income tax expense		230		287
Income from equity method investment		0		0
Net income		$ 753		$ 1,054
Earnings per share:
Basic (USD per share)		$ 0.04		$ 0.06
Diluted (USD per share)		$ 0.04		$ 0.06
Weighted average number of common shares outstanding:
Basic average common shares outstanding		0		0
Diluted average common shares outstanding		0		0