v3.5.0.1

Accrued Expenses and Other Current Liabilities - Additional Information (Details) - USD ($) $ in Millions | Apr. 30, 2016 | Apr. 30, 2015
--- | --- | ---
Other Long Term Liabilities [Member] |  |
Accrued Expenses and Other Current Liabilities [Line Items] |  |
Lease Incentive, Payable | $ 6.3 | $ 0.3
Accrued Liabilities [Member] |  |
Accrued Expenses and Other Current Liabilities [Line Items] |  |
Lease Incentive, Payable | $ 0.7 | $ 0.8

X
- Definition [Line Items] for Accrued Expenses and Other Current Liabilities [Table] + References No definition available. + Details
Name: | bv_AccruedExpensesandOtherCurrentLiabilitiesLineItems
Namespace Prefix: | bv_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition This item represents an incentive or inducement contractually stipulated between parties to a lease whereby the lessor has committed to provide the entity (lessee) with a cash payment as inducement to enter the lease. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.15(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15(5)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_LeaseIncentivePayableCurrentAndNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=bv_OtherLongTermLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_AccruedLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |