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v3.21.2

Revenue - Additional Information (Details) $ in Millions | 9 Months Ended
--- | ---
Jun. 30, 2021 USD ($)
Disaggregation Of Revenue [Line Items] |
Revenue, remaining performance obligations, amount | $ 306.2
Contract with customer billed revenue | 89.4
Contract with customer unbilled revenue additions | $ 91.4
Revenue, practical expedient, financing component | true
Minimum | Maintenance Services |
Disaggregation Of Revenue [Line Items] |
Recurring annual contract period | 1 year
Maximum | Maintenance Services |
Disaggregation Of Revenue [Line Items] |
Recurring annual contract period | 3 years

X
- Definition Contract with customer billed revenue. + References No definition available. + Details
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Namespace Prefix: | bv_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Contract with customer unbilled revenue additions. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Recurring annual contract period. + References No definition available. + Details
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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. + Details
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- Definition Indicates (true false) whether practical expedient was elected not to adjust consideration for effect of financing component when transfer and customer payment for product or service occurs within one year or less. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130569-203045 + Details
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Period Type: | duration

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- Definition Amount of transaction price allocated to performance obligation that has not been recognized as revenue. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 13 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130556-203045 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |