Name:	bwinb_CollateralHeldThatIsEqualToUltimateLossesThatWouldBePaidOrDueInEventOfInsuredSDefault
Namespace Prefix:	bwinb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Amount of assets held either as collateral or by third parties that, upon the occurrence of any triggering event or condition under the guarantee, the guarantor can obtain and liquidate to recover all or a portion of the amounts paid under the guarantee.

No definition available.

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

Number of directors of the company that are executive officers, directors, and owners.

No definition available.

Name:	bwinb_NumberOfDirectorsThatAreExecutiveOfficersDirectorsAndOwners
Namespace Prefix:	bwinb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

This element represent the number of partnership investment.

No definition available.

Name:	bwinb_NumberOfPartnershipsInvestment
Namespace Prefix:	bwinb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The estimated amount recoverable as of the balance sheet date due from first individual reinsurers for claims paid or incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported, and policy benefits, net of any related valuation allowance.

No definition available.

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

The estimated amount recoverable as of the balance sheet date due from second reinsurers for claims paid or incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported, and policy benefits, net of any related valuation allowance.

No definition available.

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

The percentage of uncollateralized exposure to shareholder's equity related to a major customer.

No definition available.

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

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570

Name:	us-gaap_EquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount before valuation allowance recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

No definition available.