Weighted Average Shares and Net Income Per Share - Calculations of Basic and Diluted Weighted Average Shares (Detail) - USD ($)	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net Income	$ 11,778,000	$ 8,775,000
Basic:
Weighted average common shares outstanding	18,922,000	18,811,000
Net Income per share	$ 0.62	$ 0.47
Diluted:
Weighted average common shares outstanding	18,922,000	18,811,000
Treasury stock impact of stock options	180,000	189,000
Total common and common equivalent shares	19,102,000	19,000,000
Net Income per share	$ 0.62	$ 0.46