Condensed Consolidated Statements of Earnings (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Consolidated Statements of Earnings (unaudited) [Abstract]
Net sales	$ 163,687	$ 147,082	$ 325,097	$ 284,810
Cost of sales	110,221	100,321	220,172	193,620
Gross margin	53,466	46,761	104,925	91,190
Operating expenses:
Selling expenses	14,495	13,569	28,554	27,281
Research and development expenses	3,230	2,280	5,799	4,095
General and administrative expenses	8,122	6,081	15,541	12,280
Total operating expenses	25,847	21,930	49,894	43,656
Earnings from operations	27,619	24,831	55,031	47,534
Other expenses (income):
Interest income	(3)	(2)	(5)	(3)
Interest expense	2,268	1,891	4,144	3,690
Other, net	293	382	654	578
Earnings before income tax expense	25,061	22,560	50,238	43,269
Income tax expense	5,382	6,024	11,213	11,216
Net earnings	$ 19,679	$ 16,536	$ 39,025	$ 32,053
Net earnings per common share - basic (in dollars per share)	$ 0.61	$ 0.52	$ 1.22	$ 1.01
Net earnings per common share - diluted (in dollars per share)	$ 0.61	$ 0.51	$ 1.21	$ 1.00