Condensed Consolidated Statements of Earnings (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Consolidated Statements of Earnings (unaudited) [Abstract]
Net sales	$ 155,043	$ 150,716	$ 480,140	$ 435,526
Cost of sales	107,041	104,535	327,213	298,155
Gross margin	48,002	46,181	152,927	137,371
Operating expenses:
Selling expenses	14,229	13,656	42,783	40,937
Research and development expenses	2,540	2,712	8,339	6,807
General and administrative expenses	5,768	6,758	21,309	19,038
Total operating expenses	22,537	23,126	72,431	66,782
Earnings from operations	25,465	23,055	80,496	70,589
Other expenses (income):
Interest income	(4)	(2)	(9)	(5)
Interest expense	1,801	2,012	5,945	5,702
Other, net	139	348	793	926
Earnings before income tax expense	23,529	20,697	73,767	63,966
Income tax expense	4,315	4,654	15,528	15,870
Net earnings	$ 19,214	$ 16,043	$ 58,239	$ 48,096
Net earnings per common share - basic (in dollars per share)	$ 0.60	$ 0.50	$ 1.82	$ 1.51
Net earnings per common share - diluted (in dollars per share)	$ 0.59	$ 0.50	$ 1.79	$ 1.49