Adjusted LIBOR rate

No definition available.

Name:	bro_AdjustedLiborRate
Namespace Prefix:	bro_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Extension Period

+ References

No definition available.

+ Details

Name:	bro_DebtInstrumentExtensionPeriod
Namespace Prefix:	bro_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Number of Extension Periods

+ References

No definition available.

+ Details

Name:	bro_DebtInstrumentNumberofExtensionPeriods
Namespace Prefix:	bro_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument, revolving and term loan

+ References

No definition available.

+ Details

Name:	bro_DebtInstrumentRevolvingAndTermLoan
Namespace Prefix:	bro_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Unsecured Revolving Credit Facility

+ References

No definition available.

+ Details

Name:	bro_UnsecuredRevolvingCreditFacility
Namespace Prefix:	bro_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

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

+ References

+ 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

Amount of the required periodic payments including both interest and principal payments.

+ References

+ Details

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

- Definition

Amount of the required periodic payments applied to interest.

+ References

+ Details

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

- Definition

Amount of the required periodic payments applied to principal.

+ References

+ Details

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

- Definition

Amount, after accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the 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))
-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 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
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 the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: 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)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

+ Details

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

- Definition

Amount of cash outflow for cost from early extinguishment and prepayment of debt. Includes, but is not limited to, third-party cost, premium paid, and other fee paid to lender directly for debt extinguishment or debt prepayment. Excludes accrued interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

+ Details

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

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

+ Details

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

- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Definition

Carrying value as of the balance sheet date of the portion of long-term notes having the highest claim on the assets of the issuer in case of bankruptcy or liquidation, due within one year or the normal operating cycle, if longer. Senior note holders are paid off in full before any payments are made to debt holders having a lesser priority of repayment.

+ References

+ Details

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

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: 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)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: 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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Carrying value as of the balance sheet date of uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

+ References

+ Details

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

- Definition

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=bro_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TradingActivityByTypeAxis=bro_MasterAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis=bro_SeriesCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis=bro_SeriesDMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis=bro_SeriesEMember
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_CreditFacilityAxis=us-gaap_LongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=bro_TermLoanMember
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_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt - Narrative (Detail)			3 Months Ended			12 Months Ended
Long-Term Debt - Narrative (Detail)	Dec. 21, 2018 USD ($)	May 20, 2014 USD ($) extension	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2019 USD ($)	Nov. 15, 2018 USD ($)	May 10, 2018 USD ($)	Jun. 28, 2017 USD ($)	Dec. 22, 2016 USD ($)	Jan. 15, 2015 USD ($)	Sep. 18, 2014 USD ($)	Apr. 17, 2014 USD ($)	Sep. 15, 2011 USD ($)	Feb. 01, 2008 USD ($)	Dec. 22, 2006 USD ($)
Debt Instrument [Line Items]
Proceeds from Issuance of Debt				$ 2,800,000
Write off of Deferred Debt Issuance Cost				200,000
Debt Issuance Costs, Noncurrent, Net												$ 1,600,000
Credit facility, outstanding amount			$ 965,000,000			$ 965,000,000	$ 365,000,000
Revolving and term loan						1,015,000,000.0
Potential increased in line of credit facility																$ 500,000,000.0
Unsecured revolving credit facility			350,000,000.0			350,000,000.0				$ 600,000,000.0		$ 400,000,000.0				800,000,000.0
Debt Instrument, Periodic Payment, Principal			5,000,000.0
Unsecured term loans			365,000,000.0			365,000,000.0										550,000,000.0
Long-term Debt, Maturities, Repayments of Principal in Year Two			55,000,000.0			55,000,000.0
Debt Instrument, Periodic Payment	$ 250,000,000.0
Proceeds from lines of credit						600,000,000	0	$ 0
Outstanding debt balance			1,506,990,000			1,506,990,000	$ 976,141,000
Senior Notes Due Two Thousand Sixteen [Member]
Debt Instrument [Line Items]
Current portion of senior notes														$ 25,000,000.0
5.370% senior notes, Series D, quarterly interest payments, balloon due 2015
Debt Instrument [Line Items]
Current portion of senior notes													$ 25,000,000.0
Credit Agreement
Debt Instrument [Line Items]
Number of extension periods \| extension		2
Extension period		1 year
Unsecured revolving credit facility																$ 1,350,000,000.0
Unsecured Senior Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage															4.20%
Debt instrument, face amount															$ 500,000,000.0
Outstanding debt balance			500,000,000.0			500,000,000.0
Term Loan
Debt Instrument [Line Items]
Credit facility, outstanding amount		$ 550,000,000.0
Debt Instrument, Periodic Payment, Principal				67,500,000
Unsecured term loans			$ 300,000,000.0			$ 300,000,000.0
Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility, outstanding amount		$ 375,000,000.0													$ 475,000,000.0
Master Agreement \| Series C
Debt Instrument [Line Items]
Unsecured senior notes outstanding																		$ 25,000,000.0	$ 25,000,000.0
Debt instrument interest rate stated percentage																			5.66%
Master Agreement \| Series D
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage																		5.37%
Master Agreement \| Series E
Debt Instrument [Line Items]
Unsecured senior notes outstanding											$ 100,000,000.0						$ 100,000,000.0
Debt Instrument, Periodic Payment, Interest					$ 700,000
Debt instrument interest rate stated percentage																	4.50%
Long-term Debt, Contingent Payment of Principal or Interest				$ 700,000
LIBOR \| Term Loan
Debt Instrument [Line Items]
30-day Adjusted LIBOR Rate			2.50%			2.50%
LIBOR \| Revolving Credit Facility
Debt Instrument [Line Items]
30-day Adjusted LIBOR Rate			2.563%			2.563%
LIBOR \| Long-term Debt [Member]
Debt Instrument [Line Items]
30-day Adjusted LIBOR Rate			2.288%			2.288%
Minimum
Debt Instrument [Line Items]
Debt instrument, variable interest rate						1.00%
Minimum \| Term Loan
Debt Instrument [Line Items]
Unsecured term loans	300,000,000.0
Minimum \| Revolving Credit Facility
Debt Instrument [Line Items]
Facility fee						0.15%
Minimum \| LIBOR \| Term Loan
Debt Instrument [Line Items]
Debt instrument, variable interest rate						1.00%
Minimum \| LIBOR \| Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, variable interest rate						0.85%
Maximum
Debt Instrument [Line Items]
Debt instrument, variable interest rate						1.75%
Maximum \| Term Loan
Debt Instrument [Line Items]
Unsecured term loans	$ 450,000,000.0
Maximum \| Revolving Credit Facility
Debt Instrument [Line Items]
Facility fee						0.25%
Maximum \| LIBOR \| Term Loan
Debt Instrument [Line Items]
Debt instrument, variable interest rate						1.75%
Maximum \| LIBOR \| Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, variable interest rate						1.50%
Scenario, Forecast [Member]
Debt Instrument [Line Items]
Unsecured senior notes outstanding									$ 5,000,000.0
Subsequent Event [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year Two									$ 3,800,000