Weighted Average Shares and Net Income Per Share - Calculations of Basic and Diluted Weighted Average Common Shares (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net Income	$ 12,871,000	$ 12,789,000	$ 26,278,000	$ 24,567,000
Basic:
Weighted average common shares outstanding	18,452,000	18,877,000	18,488,000	18,899,000
Net Income per share	$ 0.70	$ 0.68	$ 1.42	$ 1.30
Diluted:
Weighted average common shares outstanding	18,452,000	18,877,000	18,488,000	18,899,000
Treasury stock impact of stock options	319,000	212,000	291,000	196,000
Total common and common equivalent shares	18,771,000	19,089,000	18,779,000	19,095,000
Net Income per share	$ 0.69	$ 0.67	$ 1.40	$ 1.29