Condensed Consolidated Statements of Earnings - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Net sales	$ 157,029	$ 161,410
Cost of sales	107,934	109,951
Gross margin	49,095	51,459
Operating expenses:
Selling expenses	14,126	14,059
Research and development expenses	2,895	2,569
General and administrative expenses	5,594	7,591
Total operating expenses	22,615	24,219
Earnings from operations	26,480	27,240
Other expenses:
Interest expense, net	1,589	1,874
Other, net	98	189
Total other expenses (income)	1,687	2,063
Earnings before income tax expense	24,793	25,177
Income tax expense	6,010	5,831
Net earnings	$ 18,783	$ 19,346
Net earnings per common share - basic (in dollars per share)	$ 0.58	$ 0.60
Net earnings per common share - diluted (in dollars per share)	$ 0.58	$ 0.60