Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 402,440	$ 393,761	$ 377,698
Cost of sales	246,694	243,185	241,922
Gross margin	155,746	150,576	135,776
Selling, engineering and administration	100,124	99,811	93,407
Operating earnings	55,622	50,765	42,369
Interest expense, net	789	921	1,217
Earnings before income taxes	54,833	49,844	41,152
Provision for income taxes	20,262	17,549	15,214
Net earnings	$ 34,571	$ 32,295	$ 25,938
Earnings per share:
Basic (in dollars per share)	$ 1.20	$ 1.12	$ 0.90
Diluted (in dollars per share)	$ 1.19	$ 1.11	$ 0.90
Shares used in computation of earnings per share:
Basic (in shares)	28,927	28,887	28,759
Impact of dilutive securities (in shares)	184	163	135
Diluted (in shares)	29,111	29,050	28,894