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