Stock-Based Compensation and Stock Options - Stock Compensation Expense for Time Based Options and Performance Based Options (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Effect on basic earnings per share	$ 0.66	$ 0.70	$ 1.12	$ 1.42
Effect on diluted earnings per share	$ 0.65	$ 0.69	$ 1.11	$ 1.40
Time Based Options and Performance Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total cost of stock-based compensation included in income before income tax provision	$ 1,238,000	$ 1,198,000	$ 2,233,000	$ 2,423,000
Amount of income tax benefit recognized	(255,000)	(249,000)	(492,000)	(528,000)
Amount charged against net income	$ 983,000	$ 949,000	$ 1,741,000	$ 1,895,000
Effect on basic earnings per share	$ (0.05)	$ (0.05)	$ (0.10)	$ (0.10)
Effect on diluted earnings per share	$ (0.05)	$ (0.05)	$ (0.10)	$ (0.10)
Time Based Options and Performance Based Options [Member] | Cost of Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total cost of stock-based compensation included in income before income tax provision	$ 506,000	$ 518,000	$ 994,000	$ 1,002,000
Time Based Options and Performance Based Options [Member] | General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total cost of stock-based compensation included in income before income tax provision	$ 732,000	$ 680,000	$ 1,239,000	$ 1,421,000