Subsequent Events (Details) - Subsequent Event [Member]	Aug. 02, 2016 $ / shares
Subsequent Event [Line Items]
Maximum stock option exercise price	$ 6.11
Number of eligible participants	113
Number of options exchanged	599,517
Percent exchanged	68.30%
Replacement options granted	241,399

Maximum stock option exercise price

No definition available.

Name:	bv_Maximumstockoptionexerciseprice
Namespace Prefix:	bv_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of participants eligible to participate in option exchange program.

+ References

No definition available.

+ Details

Name:	bv_Numberofeligibleparticipants
Namespace Prefix:	bv_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of options exchanged as part of the option exchange program.

+ References

No definition available.

+ Details

Name:	bv_Numberofoptionsexchanged
Namespace Prefix:	bv_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percent of the total number of shares underlying the eligible options that were exchanged as part of the option exchange program.

+ References

No definition available.

+ Details

Name:	bv_Percentexchanged
Namespace Prefix:	bv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of replacement options granted as part of option exchange program.

+ References

No definition available.

+ Details

Name:	bv_Replacementoptionsgranted
Namespace Prefix:	bv_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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

- Details

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