Common Stock and Stock Plans - Summary of Employee Stock Options and Employee Stock Purchase Plan Weighted Average Assumptions (Detail)	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	30.40%	33.40%	32.90%
Risk-free interest rate	1.90%	1.70%	1.70%
Dividend yield	0.00%	0.00%	0.00%
Expected life	5 years 4 months 24 days	5 years 6 months	5 years 6 months
TSR Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	27.50%
Risk-free interest rate	1.90%
Dividend yield	0.00%
Expected life	5 years
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	22.00%	31.10%	24.60%
Risk-free interest rate	1.30%	0.50%	0.30%
Dividend yield	0.00%	0.00%	0.00%
Expected life	6 months	6 months	6 months

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

+ Details

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- Definition

Weighted average expected volatility rate of share-based compensation awards.

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- Definition

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.

+ References

No definition available.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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