Quarterly Results (Unaudited) - Summary of Unaudited Quarterly Results of Operations (Detail) (USD $)	3 Months Ended								12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 120,246,000	$ 121,098,000	$ 119,359,000	$ 118,113,000	$ 111,959,000	$ 107,287,000	$ 105,458,000	$ 104,606,000	$ 478,816,000	$ 429,310,000	$ 412,668,000
Gross Profit	26,537,000	27,706,000	27,320,000	26,918,000	23,909,000	21,734,000	22,836,000	23,181,000	108,481,000	91,660,000	93,842,000
Net income	$ 8,333,000	$ 8,775,000	$ 8,675,000	$ 8,609,000	$ 7,580,000	$ 5,924,000	$ 6,630,000	$ 6,596,000	$ 34,392,000	$ 26,730,000	$ 26,552,000
Net Income per Basic Common Share	$ 0.40	$ 0.42	$ 0.41	$ 0.40	$ 0.35	$ 0.27	$ 0.30	$ 0.29	$ 1.63	$ 1.20	$ 1.16
Net Income per Diluted Common Share	$ 0.39	$ 0.41	$ 0.41	$ 0.40	$ 0.35	$ 0.27	$ 0.29	$ 0.29	$ 1.61	$ 1.19	$ 1.14