Losses and Loss Adjustment Reserve - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2015 Reinsurer	Dec. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Ceded rate of premiums under insurance program	100.00%bro_PercentageOfCededPremiums
Premiums written net	$ 123,110,000us-gaap_CededPremiumsWritten
Ceded unpaid loss	13,100,000
The reinsurance recoverable	304,100,000
Prepaid reinsurance premiums	291,037,000us-gaap_PrepaidReinsurancePremiums	320,586,000us-gaap_PrepaidReinsurancePremiums
Reserve for losses and loss adjustment expense	0
Number of reinsurers	3bro_NumberOfReinsurers
Homeowners
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Ceded unpaid loss	8,698
Reinsurance recoverable, incurred but not reported claims	102
Private Passenger Auto Liability
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Ceded unpaid loss	69,026
Reinsurance recoverable, incurred but not reported claims	39,424
Other Liability
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Ceded unpaid loss	5,001
Wright Flood
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Ceded rate of premiums under insurance program	100.00%
Expenses and allowance rate received in premiums	30.80%
Premiums written net	122,900,000
Wright Flood \| Quota Share Agreement
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Effective cedes rate under quota share agreement	100.00%
Commission rate, percent of ceded written premiums	30.50%
Wright Flood \| Quota Share Agreement \| Ceded Credit Risk, Concentrated Credit Risk
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Ceded amount	$ 200,000

Number of reinsurers.

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- Definition

Percentage of ceded premiums.

+ References

No definition available.

+ Details

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- Definition

Percentage of flood premiums ceded.

+ References

No definition available.

+ Details

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- Definition

Percentage of reinsurance recoverables allowance.

+ References

No definition available.

+ Details

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- Definition

Reinsurance percentage of ceding commission.

+ References

No definition available.

+ Details

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- Definition

Reserve For Losses And Loss Adjustment Expenses For Reinsurance Liability

+ References

No definition available.

+ Details

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- Definition

Amount of written premiums ceded to other entities.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 1

-Subparagraph (b),(c)(2)

-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

+ Details

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- Definition

The unexpired portion of premiums ceded on policies in force as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Prepaid Reinsurance Premiums

-URI http://asc.fasb.org/extlink&oid=6521719

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 340

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6485982&loc=d3e22818-158507

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- Definition

Estimated amount after valuation allowance of reinsurance recoverables, due from reinsurers for incurred claims not yet reported, and claims settlement expenses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21412-158489

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 6

-Article 7

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Amount after valuation allowance recoverable including premium paid 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.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 6

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 20

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.(a),6)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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- Definition

Amount after valuation allowance of reinsurance recoverables for losses reported to the ceding insurer but not yet paid, amounts expected of incurred losses and settlement expenses, which have not yet been reported to the ceding insurer.

+ References

+ Details

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- Definition

Amount before valuation allowance of reinsurance recoverables for losses reported to the ceding insurer but not yet paid, and for amounts expected based upon statistical projections and other measures of incurred losses and loss settlement expenses which have not yet been reported to the ceding insurer.

+ References

No definition available.

+ Details

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- Details

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