Quarterly Financial Data (Unaudited) - Summarized unaudited quarterly financial data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 49,994	$ 49,284	$ 57,576	$ 72,541	$ 48,632	$ 50,086	$ 60,479	$ 74,194	$ 229,395	$ 233,391	$ 227,829
Gross profit	16,939	17,100	18,459	23,772	17,463	16,889	19,252	24,013	76,270	77,617	77,121
Income from operations	7,819	7,666	4,290	7,838	7,142	7,047	6,532	7,497	27,613	28,218	27,005
Net income	$ 4,951	$ 4,797	$ 2,732	$ 4,973	$ 4,526	$ 4,541	$ 4,150	$ 4,755	$ 17,453	$ 17,972	$ 17,165
Diluted net income per common share (in dollars per share)	$ 0.25	$ 0.24	$ 0.14	$ 0.25	$ 0.23	$ 0.23	$ 0.21	$ 0.24	$ 0.87	$ 0.90	$ 0.86