Quarterly Results (Unaudited) - Summary of Unaudited Quarterly Results of Operations (Detail) (USD $)	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]
Revenues	$ 122,195,000	$ 122,352,000	$ 123,714,000	$ 124,364,000	$ 120,246,000	$ 121,098,000	$ 119,359,000	$ 118,113,000	$ 492,625,000	$ 478,816,000	$ 429,310,000
Gross Profit	22,674,000	24,128,000	25,467,000	27,700,000	26,537,000	27,706,000	27,320,000	26,918,000	99,969,000	108,481,000	91,660,000
Net Income	$ 5,576,000	$ 6,832,000	$ 7,883,000	$ 8,299,000	$ 8,333,000	$ 8,775,000	$ 8,675,000	$ 8,609,000	$ 28,590,000	$ 34,392,000	$ 26,730,000
Net Income per Basic Common Share	$ 0.27	$ 0.33	$ 0.38	$ 0.40	$ 0.40	$ 0.42	$ 0.41	$ 0.40	$ 1.38	$ 1.63	$ 1.20
Net Income per Diluted Common Share	$ 0.27	$ 0.33	$ 0.37	$ 0.39	$ 0.39	$ 0.41	$ 0.41	$ 0.40	$ 1.37	$ 1.61	$ 1.19