Stock-Based Compensation and Stock Options - Outstanding Options (Detail) - USD ($)	3 Months Ended	9 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance, Shares	1,053,307	1,169,871	1,064,439	1,143,928
Granted, Number of Options	145,150	154,500	261,750	305,550
Exercised, Number of Options	(76,122)	(51,712)	(197,230)	(263,544)
Cancelled - forfeited, Number of Options	(408)
Cancelled - expired, Number of Options	(400)
Options outstanding, ending balance, Shares	1,121,527		1,121,527
Ending vested and expected to vest, Number of Options	952,332		952,332
Ending exercisable, Number of Options	377,905		377,905
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 41.81	$ 38.41	$ 39.45	$ 32.02
Granted, Weighted Average Exercise Price per Share	59.32	57.75	56.72	52.49
Exercised, Weighted Average Exercise Price per Share	41.73	$ 31.15	35.94	$ 26.96
Cancelled - forfeited, Weighted Average Exercise Price per Share	38.94
Cancelled - expired, Weighted Average Exercise Price per Share	41.82
Options outstanding, ending balance, Weighted Average Exercise Price	44.08		44.08
Ending vested and expected to vest, Weighted Average Exercise Price per Share	41.68		41.68
Ending exercisable, Weighted Average Exercise Price per Share	$ 33.57		$ 33.57
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 6 months 10 days
Ending vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 5 months 8 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 8 months 23 days
Option outstanding, Aggregate Intrinsic Value	$ 19,778,926		$ 19,778,926
Ending vested and expected to vest, Aggregate Intrinsic Value	19,132,688		19,132,688
Ending exercisable, Aggregate Intrinsic Value	$ 10,639,330		$ 10,639,330

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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