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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Effect on diluted net income per share	$ 0.41	$ 0.37	$ 0.75	$ 0.77
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	$ 488,000	$ 445,000	$ 1,104,000	$ 1,162,000
Amount of income tax benefit recognized	(188,000)	(169,000)	(425,000)	(442,000)
Amount charged against net income	$ 300,000	$ 276,000	$ 679,000	$ 720,000
Effect on diluted net income per share	$ (0.01)	$ (0.01)	$ (0.03)	$ (0.03)
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	$ 321,000	$ 255,000	$ 633,000	$ 494,000
Time Based Options and Performance Based Options [Member] | General and administrative expenses [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	$ 167,000	$ 190,000	$ 471,000	$ 668,000