Weighted Average Shares and Net Income Per Share - Calculations of Basic and Diluted Weighted Average Shares (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Income	$ 10,298,000	$ 9,569,000	$ 34,865,000	$ 26,737,000
Basic:
Weighted average common shares outstanding	18,758,000	18,849,000	18,852,000	18,806,000
Net Income per share	$ 0.55	$ 0.51	$ 1.85	$ 1.42
Diluted:
Weighted average common shares outstanding	18,758,000	18,849,000	18,852,000	18,806,000
Treasury stock impact of stock options	226,000	272,000	206,000	223,000
Total common and common equivalent shares	18,984,000	19,121,000	19,058,000	19,029,000
Net Income per share	$ 0.54	$ 0.50	$ 1.83	$ 1.41