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								12 Months Ended
	Jan. 01, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets:
Contract assets	$ 19,125	$ 23,040	$ 23,040			$ 0				$ 23,040	$ 0
Inventories	65,155	84,465				80,339				84,465	80,339
Liabilities:
Accounts payable	72,594	73,265				71,931				73,265	71,931
Deferred revenue	4,621	6,990								6,990
Deferred tax liabilities	15,185	39,265				14,714				39,265	14,714
Stockholders' equity:
Retained earnings	376,381	411,325				374,783				411,325	374,783
Accumulated other comprehensive loss		(42,685)				(20,148)				(42,685)	(20,148)
Income Statement
Net sales		209,938	197,886	$ 186,413	$ 191,660	178,030	$ 180,041	$ 174,879	$ 165,487	785,897	698,437	$ 566,852
Cost of sales										633,252	535,078	428,048
Gross profit		41,872	35,139	36,127	39,507	39,480	40,054	43,327	40,498	152,645	163,359	138,804
Selling, product development and administrative expenses										103,457	97,159	83,359
Operating income										49,188	66,200	55,445
Interest expense										6,212	2,720	1,068
Other income, net										(289)	2,161	(562)
Income before income taxes										43,265	61,319	54,939
Income tax expense										8,453	11,974	17,821
(Income) loss from equity method investment										(132)	28	(69)
Net income		$ 7,184	$ 6,256	$ 10,450	$ 11,054	$ 13,848	$ 10,675	$ 13,125	$ 11,669	$ 34,944	$ 49,317	$ 37,187
Earnings per share:
Basic (USD per share)		$ 0.42	$ 0.36	$ 0.61	$ 0.64	$ 0.81	$ 0.63	$ 0.77	$ 0.69	$ 2.03	$ 2.89	$ 2.20
Diluted (USD per share)		$ 0.42	$ 0.36	$ 0.60	$ 0.64	$ 0.80	$ 0.62	$ 0.76	$ 0.68	$ 2.02	$ 2.85	$ 2.16
Weighted average number of common shares outstanding:
Basic average common shares outstanding (shares)										17,204	17,045	16,871
Diluted average common shares outstanding (shares)										17,330	17,317	17,241
Calculated under Revenue Guidance in Effect before Topic 606
Assets:
Contract assets		$ 0				$ 0				$ 0	$ 0
Inventories		103,767				80,339				103,767	80,339
Liabilities:
Accounts payable		71,937				71,931				71,937	71,931
Deferred revenue		7,952				3,412				7,952	3,412
Deferred tax liabilities		38,422				14,714				38,422	14,714
Stockholders' equity:
Retained earnings		408,846				374,783				408,846	374,783
Accumulated other comprehensive loss		(42,735)								(42,735)
Income Statement
Net sales										781,612
Cost of sales										630,220
Gross profit										151,392
Selling, product development and administrative expenses										103,457
Operating income										47,935
Interest expense										6,212
Other income, net										(289)
Income before income taxes										42,012
Income tax expense										8,081
(Income) loss from equity method investment										(132)
Net income										$ 34,063
Earnings per share:
Basic (USD per share)										$ 1.98
Diluted (USD per share)										$ 1.97
Weighted average number of common shares outstanding:
Basic average common shares outstanding (shares)										17,204
Diluted average common shares outstanding (shares)										17,330
Accounting Standards Update 2014-09
Assets:
Contract assets	3,915
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Assets:
Contract assets		23,040				19,125				$ 23,040	19,125
Inventories		(19,302)				(15,184)				(19,302)	(15,184)
Liabilities:
Accounts payable		1,328				663				1,328	663
Deferred revenue		(962)				1,209				(962)	1,209
Deferred tax liabilities		843				471				843	471
Stockholders' equity:
Retained earnings	1,600	2,479				$ 1,598				2,479	$ 1,598
Accumulated other comprehensive loss		$ 50								50
Income Statement
Net sales	$ 19,600									4,285
Cost of sales										3,032
Gross profit										1,253
Selling, product development and administrative expenses										0
Operating income										1,253
Interest expense										0
Other income, net										0
Income before income taxes										1,253
Income tax expense										372
(Income) loss from equity method investment										0
Net income										$ 881
Earnings per share:
Basic (USD per share)										$ 0.05
Diluted (USD per share)										$ 0.05
Weighted average number of common shares outstanding:
Basic average common shares outstanding (shares)										0
Diluted average common shares outstanding (shares)										0