Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 284,178	$ 262,476	$ 836,964	$ 745,345
Cost of sales	150,282	143,338	454,881	403,866
Gross profit	133,896	119,138	382,083	341,479
Operating expenses:
Research and development and other engineering	10,441	11,265	32,840	35,051
Selling	26,879	27,867	83,653	86,150
General and administrative	36,114	33,457	112,897	105,962
Net gain on disposal of assets	(460)	(147)	(1,769)	(147)
Total operating expenses	72,974	72,442	227,621	227,016
Income from operations	60,922	46,696	154,462	114,463
Loss in equity method investment, before tax	(30)	(13)	(52)	(53)
Interest expense, net	(58)	(296)	(332)	(685)
Gain (adjustment) on bargain purchase of a business	0	(2,052)	0	6,336
Gain on disposal of a business	0	443	0	443
Income before taxes	60,834	44,778	154,078	120,504
Provision for income taxes	16,473	16,581	40,202	40,972
Net income	$ 44,361	$ 28,197	$ 113,876	$ 79,532
Earnings per common share:
Basic (in dollars per share)	$ 0.96	$ 0.60	$ 2.46	$ 1.67
Diluted (in dollars per share)	$ 0.95	$ 0.59	$ 2.43	$ 1.66
Number of shares outstanding
Basic (in shares)	46,192	47,367	46,375	47,544
Diluted (in shares)	46,622	47,686	46,770	47,843
Cash dividends declared per common share (in dollars per share)	$ 0.220	$ 0.42	$ 0.650	$ 0.81