v3.8.0.1

Subsequent Events (Details) - Subsequent Event [Member] - USD ($) $ / shares in Units, $ in Millions | 1 Months Ended |
--- | --- | ---
Nov. 28, 2017 | Nov. 26, 2017
Subsequent Event [Line Items] |  |
Business Acquisition, Share Price |  | $ 5.50
Business Combination Unvested Equity Awards Not Converted |  | 70.00%
Business Combination Percent of Unvested Equity Awards Converted |  | 30.00%
Business Combination Termination Fee Acquiree | $ 18.3 |
Business Combination Termination Fee Acquierer | $ 26.1 |

X
- Definition The percentage of equity awards that are converted into a right to receive the per share purchase price upon completion of the merger. + References No definition available. + Details
Name: | bv_BusinessCombinationPercentofUnvestedEquityAwardsConverted
Namespace Prefix: | bv_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Termination fee to be paid by the acquirer in the event the acquirer terminates the merger agreement. + References No definition available. + Details
Name: | bv_BusinessCombinationTerminationFeeAcquierer
Namespace Prefix: | bv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Termination fee to be paid by acquiree in the event the acquiree terminates the merger agreement. + References No definition available. + Details
Name: | bv_BusinessCombinationTerminationFeeAcquiree
Namespace Prefix: | bv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The percentage of equity awards that are not converted into a right to receive the per share purchase price upon completion of the merger. + References No definition available. + Details
Name: | bv_BusinessCombinationUnvestedEquityAwardsNotConverted
Namespace Prefix: | bv_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination. + References No definition available. + Details
Name: | us-gaap_BusinessAcquisitionSharePrice
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |