v3.7.0.1

Acquired Intangible Assets, net - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Apr. 30, 2017 | Apr. 30, 2016 | Apr. 30, 2015
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization Of Intangible Assets Including Portion In Cost Of Revenue | $ 1.9 | $ 1.9 | $ 1.9

X
- Definition Amortization of intangible assets including amount related to developed technology which is included in cost of revenue on the statement of operations. + References No definition available. + Details
Name: | bv_AmortizationOfIntangibleAssetsIncludingPortionInCostOfRevenue
Namespace Prefix: | bv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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
Name: | us-gaap_FiniteLivedIntangibleAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration