Long-Term Debt - Long-Term Debt Instrument (Additional Information) (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2016	Dec. 31, 2015
5.660% senior notes, Series C, semi-annual interest payments, balloon due 2016
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.66%	5.66%
Debt instrument maturity year	2016	2016
4.500% senior notes, Series E, quarterly interest payments, balloon due 2018
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.50%	4.50%
Debt instrument maturity year	2018	2018
4.200% senior notes, semi-annual interest payments, balloon due 2024
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.20%	4.20%
Debt instrument maturity year	2024	2024
5-year term-loan facility, periodic interest and principal payments, LIBOR plus up to 1.75%, expires May 20, 2019
Debt Instrument [Line Items]
Line of credit facility, expiration period	5 years	5 years
Line of credit facility, expiration date	May 20, 2019	May 20, 2019
5-year term-loan facility, periodic interest and principal payments, LIBOR plus up to 1.75%, expires May 20, 2019 \| LIBOR
Debt Instrument [Line Items]
Debt instrument, variable interest rate	1.75%	1.75%
Five Year Term Loan Facility Expires In Two Thousand Ninteen Current [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.20%	0.20%
Debt instrument maturity year	2019	2019
5-year revolving-loan facility, periodic interest payments, currently LIBOR plus up to 1.50%, plus commitment fees up to 0.25%, expires May 20, 2019
Debt Instrument [Line Items]
Line of credit facility, expiration period	5 years	5 years
Line of credit facility, commitment fee percentage	0.25%	0.25%
Line of credit facility, expiration date	May 20, 2019	May 20, 2019
5-year revolving-loan facility, periodic interest payments, currently LIBOR plus up to 1.50%, plus commitment fees up to 0.25%, expires May 20, 2019 \| LIBOR
Debt Instrument [Line Items]
Debt instrument, variable interest rate	1.50%	1.50%
Revolving credit loan, quarterly interest payments, LIBOR plus up to 1.40% and availability fee up to 0.25%, expires December 31, 2016
Debt Instrument [Line Items]
Line of credit facility, expiration date	Dec. 31, 2016	Dec. 31, 2016
Maximum \| Revolving credit loan, quarterly interest payments, LIBOR plus up to 1.40% and availability fee up to 0.25%, expires December 31, 2016
Debt Instrument [Line Items]
Line of credit facility, commitment fee percentage	0.25%	0.25%
Maximum \| Revolving credit loan, quarterly interest payments, LIBOR plus up to 1.40% and availability fee up to 0.25%, expires December 31, 2016 \| LIBOR
Debt Instrument [Line Items]
Debt instrument, variable interest rate	1.40%	1.40%
Wells Fargo [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	$ 800,000	$ 800,000

Debt Instruments Maturity Year

No definition available.

Name:	bro_DebtInstrumentsMaturityYear
Namespace Prefix:	bro_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_FivePointSixSixZeroPercentSeniorNotesDueTwoThousandSixteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_FourPointFiveZeroZeroPercentSeniorNotesDueTwoThousandEighteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_FourPointTwoZeroZeroPercentSeniorNotesDueTwoThousandTwentyFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_FiveYearTermLoanFacilityExpiresInTwoThousandNinteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_FiveYearTermLoanFacilityExpiresInTwoThousandNinteenCurrentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_FiveYearRevolvingLoanFacilityExpiresInTwoThousandNinteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_RevolvingCreditLoanExpiresInTwoThousandSixteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=bro_WellsFargoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: