Quarterly Financial Data (Unaudited) - Summarized unaudited quarterly financial data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 63,032	$ 52,866	$ 60,791	$ 72,487	$ 55,392	$ 50,933	$ 56,725	$ 71,634	$ 249,176	$ 234,684	$ 229,395
Gross profit	22,155	16,643	18,064	22,452	17,663	16,754	18,913	22,966	79,314	76,296	76,270
Income from operations	11,697	7,655	7,731	10,400	8,585	7,622	7,090	9,091	37,483	32,388	27,613
Net income	$ 7,503	$ 4,823	$ 4,899	$ 6,594	$ 5,418	$ 4,890	$ 4,502	$ 5,757	$ 23,819	$ 20,567	$ 17,453
Diluted net income per common share (in dollars per share)	$ 0.37	$ 0.24	$ 0.24	$ 0.32	$ 0.27	$ 0.24	$ 0.22	$ 0.29	$ 1.17	$ 1.02	$ 0.87