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Summary of Significant Accounting Policies - Schedule of Allowance for Credit Losses (Parenthetical) (Detail) $ in Millions | Mar. 31, 2019 USD ($)
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Accounting Policies [Abstract] |
Allowance for bad debt expense | $ 8.7

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- Definition Allowance for bad debt. + References No definition available. + Details
Name: | qnst_AllowanceForBadDebt
Namespace Prefix: | qnst_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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