Summary of Significant Accounting Policies (Details)	3 Months Ended
Mar. 31, 2013
Summary of Significant Accounting Policies [Abstract]
Percentage of decline on cost of securities treated as other-than-temporary impairment (in hundredths)	20.00%
Period of decline on the cost of equity securities that will be considered other-than-temporary impairment	6 months

This line item represents percentage of original or adjusted cost exceeding unrealized loss for any equity security during the reporting period.

No definition available.

Name:	bwinb_PercentageOfAdjustedCostExceedingUnrealizedLoss
Namespace Prefix:	bwinb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration