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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Income	$ 11,865,000	$ 12,871,000	$ 20,167,000	$ 26,278,000
Basic:
Weighted average common shares outstanding	17,937,000	18,452,000	17,960,000	18,488,000
Net Income per share	$ 0.66	$ 0.70	$ 1.12	$ 1.42
Diluted:
Weighted average common shares outstanding	17,937,000	18,452,000	17,960,000	18,488,000
Treasury stock impact of stock options	237,000	319,000	184,000	291,000
Total common and common equivalent shares	18,174,000	18,771,000	18,144,000	18,779,000
Net Income per share	$ 0.65	$ 0.69	$ 1.11	$ 1.40