Condensed Consolidated Statements of Earnings (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidated Statements of Earnings (unaudited) [Abstract]
Net sales	$ 161,410	$ 137,728
Cost of sales	109,951	93,299
Gross margin	51,459	44,429
Operating expenses:
Selling expenses	14,059	13,712
Research and development expenses	2,569	1,815
General and administrative expenses	7,419	6,199
Total operating expenses	24,047	21,726
Earnings from operations	27,412	22,703
Other expenses (income):
Interest income	(2)	(2)
Interest expense	1,876	1,799
Other, net	361	196
Earnings before income tax expense	25,177	20,710
Income tax expense	5,831	5,192
Net earnings	$ 19,346	$ 15,518
Net earnings per common share - basic (in dollars per share)	$ 0.60	$ 0.49
Net earnings per common share - diluted (in dollars per share)	$ 0.60	$ 0.48