Consolidated Statements of Income - USD ($)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenues	$ 518,686,000	$ 503,584,000	$ 492,625,000
Cost of revenues	413,894,000	399,040,000	392,656,000
Gross profit	104,792,000	104,544,000	99,969,000
General and administrative	57,243,000	58,484,000	54,405,000
Income before income taxes	47,549,000	46,060,000	45,564,000
Income tax provision	18,070,000	17,535,000	16,974,000
Net income	$ 29,479,000	$ 28,525,000	$ 28,590,000
Net income per share:
Basic	$ 1.52	$ 1.44	$ 1.38
Diluted	$ 1.51	$ 1.43	$ 1.37
Weighted average shares outstanding:
Basic	19,418,000	19,826,000	20,669,000
Diluted	19,570,000	20,004,000	20,890,000