Consolidated Statements of Income - USD ($)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenues	$ 595,740,000	$ 558,350,000	$ 518,686,000
Cost of revenues	470,931,000	451,097,000	413,894,000
Gross profit	124,809,000	107,253,000	104,792,000
General and administrative	63,296,000	59,350,000	57,243,000
Income before income taxes	61,513,000	47,903,000	47,549,000
Income tax provision	14,810,000	12,208,000	18,070,000
Net income	$ 46,703,000	$ 35,695,000	$ 29,479,000
Net income per share:
Basic	$ 2.48	$ 1.90	$ 1.52
Diluted	$ 2.46	$ 1.87	$ 1.51
Weighted average shares outstanding:
Basic	18,794,000	18,825,000	19,418,000
Diluted	19,008,000	19,042,000	19,570,000