Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Commitments and Contingencies [Abstract]
Capitalized acquisition costs	$ 25

Expected capitalized costs related to acquisition of home office building.

No definition available.

Name:	bwinb_CapitalizedAcquisitionCosts
Namespace Prefix:	bwinb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant