Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information (unaudited)
Net sales	$ 130,143	$ 123,573	$ 113,763	$ 48,789	$ 118,810	$ 120,565	$ 107,143	$ 53,890	$ 416,268	$ 400,408	$ 303,511
Gross profit	41,678	36,644	41,521	14,131	38,551	40,865	37,010	16,437	133,974	132,863	116,326
Income before taxes	17,666	11,873	25,551	8,606	21,034	23,672	20,954	603	63,696	66,263	61,997
Net income	$ 10,101	$ 7,302	$ 16,328	$ 5,278	$ 15,141	$ 15,548	$ 13,104	$ 383	$ 38,469	$ 43,572	$ 39,352
Basic income per common share (in dollars per share)	$ 0.44	$ 0.32	$ 0.72	$ 0.23	$ 0.67	$ 0.69	$ 0.58	$ 0.02	$ 1.71	$ 1.95	$ 1.78
Earnings per common share assuming dilution (in dollars per share)	0.44	0.32	0.71	0.23	0.66	0.68	0.57	0.01	$ 1.70	$ 1.94	$ 1.77
Cash dividends paid per share (in dollars per share)	$ 0.24	$ 0.24	$ 0.24	$ 0.24	$ 0.22	$ 0.22	$ 0.22	$ 0.22