Consolidated Statements of Income - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Revenues	$ 558,350,000	$ 518,686,000	$ 503,584,000
Cost of revenues	451,097,000	413,894,000	399,040,000
Gross profit	107,253,000	104,792,000	104,544,000
General and administrative	59,350,000	57,243,000	58,484,000
Income before income taxes	47,903,000	47,549,000	46,060,000
Income tax provision	12,208,000	18,070,000	17,535,000
Net income	$ 35,695,000	$ 29,479,000	$ 28,525,000
Net income per share:
Basic	$ 1.90	$ 1.52	$ 1.44
Diluted	$ 1.87	$ 1.51	$ 1.43
Weighted average shares outstanding:
Basic	18,825,000	19,418,000	19,826,000
Diluted	19,042,000	19,570,000	20,004,000