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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Effect on basic earnings per share	$ 0.68	$ 0.45	$ 1.30	$ 0.91
Effect on diluted earnings per share	$ 0.67	$ 0.44	$ 1.29	$ 0.90
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	$ 908,000	$ 607,000	$ 2,087,000	$ 1,529,000
Amount of income tax benefit recognized	(207,000)	(185,000)	(475,000)	(466,000)
Amount charged against net income	$ 701,000	$ 422,000	$ 1,612,000	$ 1,063,000
Effect on basic earnings per share	$ (0.04)	$ (0.02)	$ (0.09)	$ (0.06)
Effect on diluted earnings per share	$ (0.04)	$ (0.02)	$ (0.08)	$ (0.06)
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	$ 446,000	$ 411,000	$ 877,000	$ 893,000
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	$ 462,000	$ 196,000	$ 1,210,000	$ 636,000