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Retirement Savings Plan - Additional Information (Detail) - USD ($) | 12 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2016
Compensation And Retirement Disclosure [Abstract] |  |  |
Employer contribution | $ 557,000 | $ 464,000 | $ 392,000

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- References No definition available. + Details
Name: | us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration