Weighted Average Shares and Net Income Per Share - Calculations of Basic and Diluted Weighted Average Shares (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net Income	$ 8,393,000	$ 6,952,000	$ 17,168,000	$ 14,443,000
Basic:
Weighted average common shares outstanding	18,759,000	19,581,000	18,785,000	19,577,000
Net Income per share	$ 0.45	$ 0.36	$ 0.91	$ 0.74
Diluted:
Weighted average common shares outstanding	18,759,000	19,581,000	18,785,000	19,577,000
Treasury stock impact of stock options	207,000	152,000	198,000	166,000
Total common and common equivalent shares	18,966,000	19,733,000	18,983,000	19,743,000
Net Income per share	$ 0.44	$ 0.35	$ 0.90	$ 0.73