Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Stock Options and Stock-Based Compensation - Stock Compensation Expense for Time Based Options and Performance Based Options (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Effect on basic earnings per share	$ 0.47	$ 0.51	$ 0.45	$ 0.47	$ 0.42	$ 0.36	$ 0.36	$ 0.38	$ 1.90	$ 1.52	$ 1.44
Effect on diluted earnings per share	$ 0.47	$ 0.50	$ 0.44	$ 0.46	$ 0.42	$ 0.36	$ 0.35	$ 0.38	$ 1.87	$ 1.51	$ 1.43
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 taxes									$ 3,164,000	$ 2,432,000	$ 2,192,000
Amount of income tax benefit recognized									1,105,000	946,000	852,000
Amount charged to net income									$ 2,059,000	$ 1,486,000	$ 1,340,000
Effect on basic earnings per share									$ 0.11	$ 0.08	$ 0.07
Effect on diluted earnings per share									$ 0.11	$ 0.08	$ 0.07
Time Based Options and Performance Based Options [Member] \| Cost of Revenue [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 taxes									$ 1,749,000	$ 1,507,000	$ 1,288,000
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 taxes									$ 1,415,000	$ 925,000	$ 904,000