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 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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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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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No definition available.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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

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Stock-Based Compensation and Stock Options - Stock Options Outstanding and Exercisable (Detail) - $ / shares	6 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Outstanding Options	1,053,307	1,063,254	1,064,439	1,068,503	1,151,722	1,143,928
Weighted Average Remaining Contractual Life	3 years 5 months 1 day
Outstanding Options - Weighted Average Exercise Price	$ 41.81	$ 40.43	$ 39.45	$ 35.28	$ 33.24	$ 32.02
Exercisable Options - Number of Exercisable Options	419,729
Exercisable Options - Weighted Average Exercise Price	$ 34.08
Range of Exercise Price, $12.71 to $32.10 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	12.71
Range of Exercise Price, upper limit	$ 32.10
Number of Outstanding Options	245,758
Weighted Average Remaining Contractual Life	2 years 8 months 26 days
Outstanding Options - Weighted Average Exercise Price	$ 25.91
Exercisable Options - Number of Exercisable Options	152,634
Exercisable Options - Weighted Average Exercise Price	$ 22.13
Range of Exercise Price, $32.11 to $40.57 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	32.11
Range of Exercise Price, upper limit	$ 40.57
Number of Outstanding Options	224,711
Weighted Average Remaining Contractual Life	2 years 8 months 19 days
Outstanding Options - Weighted Average Exercise Price	$ 35.90
Exercisable Options - Number of Exercisable Options	130,898
Exercisable Options - Weighted Average Exercise Price	$ 36.24
Range of Exercise Price, $40.58 to $46.10 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	40.58
Range of Exercise Price, upper limit	$ 46.10
Number of Outstanding Options	217,171
Weighted Average Remaining Contractual Life	2 years 9 months 25 days
Outstanding Options - Weighted Average Exercise Price	$ 44.99
Exercisable Options - Number of Exercisable Options	118,156
Exercisable Options - Weighted Average Exercise Price	$ 44.95
Range of Exercise Price, $46.11 to $57.75 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	46.11
Range of Exercise Price, upper limit	$ 57.75
Number of Outstanding Options	365,667
Weighted Average Remaining Contractual Life	4 years 7 months 2 days
Outstanding Options - Weighted Average Exercise Price	$ 54.77
Exercisable Options - Number of Exercisable Options	18,041
Exercisable Options - Weighted Average Exercise Price	$ 48.35