Quarterly Financial Data (Unaudited) - Summarized unaudited quarterly financial data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 55,392	$ 50,933	$ 56,725	$ 71,634	$ 49,994	$ 49,284	$ 57,576	$ 72,541	$ 234,684	$ 229,395	$ 233,391
Gross profit	17,663	16,754	18,913	22,966	16,939	17,100	18,459	23,772	76,296	76,270	77,617
Income from operations	8,585	7,622	7,090	9,091	7,819	7,666	4,290	7,838	32,388	27,613	28,218
Net income	$ 5,418	$ 4,890	$ 4,502	$ 5,757	$ 4,951	$ 4,797	$ 2,732	$ 4,973	$ 20,567	$ 17,453	$ 17,972
Diluted net income per common share (in dollars per share)	$ 0.27	$ 0.24	$ 0.22	$ 0.29	$ 0.25	$ 0.24	$ 0.14	$ 0.25	$ 1.02	$ 0.87	$ 0.90