Related Parties (Details) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($) Partnership Director	Jun. 30, 2017 USD ($)
New Vernon India Fund [Member]
Related Party [Abstract]
Ownership interest in limited partnership	6.00%
New Vernon Global Opportunity Fund [Member]
Related Party [Abstract]
Ownership interest in limited partnership	37.00%
New Vernon Global Opportunity Fund II [Member]
Related Party [Abstract]
Ownership interest in limited partnership	27.00%
Director [Member] \| Limited Partnerships [Member]
Related Party [Abstract]
Number of investments \| Partnership	3
Estimated aggregate value of investment in limited partnerships	$ 40,508
Number of related parties \| Director	1
Management fees and commisions	$ 372	$ 363
Director [Member] \| Investment Firm Services [Member]
Related Party [Abstract]
Number of related parties \| Director	1
Management fees and commisions	$ 54	$ 44
Market value of equity and fixed maturity securities portfolio	$ 23,880

This element represent the number of related party investments.

No definition available.

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

- Definition

Number of the Company's directors that are executive officers, directors, and owners of organizations outside of the Company.

+ References

No definition available.

+ Details

Name:	bwinb_NumberOfRelatedPartiesThatAreManagersOfOutsideEntity
Namespace Prefix:	bwinb_
Data Type:	xbrli:integerItemType
Balance Type:	na
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- Definition

The equity interest of partners or other equity holders in a limited partnership.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

Name:	bwinb_RelatedPartyAbstract
Namespace Prefix:	bwinb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transactions with related party during the financial reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the sum of all other revenue and income realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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Namespace Prefix:
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- Details

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- Details

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Namespace Prefix:
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- Details

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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=bwinb_RelatedPartyTransactionsLimitedPartnershipsMember
Namespace Prefix:
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=bwinb_RelatedPartyTransactionsInvestmentFirmServicesMember
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