Business Combinations Business Acquisitions - Pro-forma Table (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Two Thousand Sixteen Acquisition [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Weighted Average Basic Shares Outstanding, Pro Forma			272,278	275,620
Business Acquisition, Pro Forma Revenue			$ 1,789,790	$ 1,716,592
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax			428,194	414,911
Business Acquisition, Pro Forma Net Income (Loss)			$ 260,346	$ 250,783
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax, Per Share, Basic			$ 0.93	$ 0.89
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax, Per Share, Diluted			$ 0.92	$ 0.87
Pro Forma Weighted Average Shares Outstanding, Diluted			275,608	280,224
Two Thousand Eighteen Acquisition [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Weighted Average Basic Shares Outstanding, Pro Forma	270,971	272,580
Business Acquisition, Pro Forma Revenue	$ 2,259,812	$ 2,193,169
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax	504,664	503,927
Business Acquisition, Pro Forma Net Income (Loss)	$ 375,670	$ 447,796
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax, Per Share, Basic	$ 1.35	$ 1.60
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax, Per Share, Diluted	$ 1.33	$ 1.57
Pro Forma Weighted Average Shares Outstanding, Diluted	275,521	277,586

Per basic share amount of pro forma income from continuing operations, after tax, as if the business combination had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareBasic
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Per diluted share amount of pro forma income from continuing operations, after tax, as if the business combination had been completed at the beginning of a period.

+ References

+ Details

Name:	us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareDiluted
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Amount after tax of pro forma income from continuing operations as if the business combination had been completed at the beginning of a period.

+ References

+ Details

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

- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

+ Details

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

- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

+ Details

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

- Definition

The weighted average number of shares or units and dilutive common stock or unit equivalents outstanding in the calculation of proforma diluted earnings per share (earnings per unit), which is commonly presented in initial public offerings based on the terms of the offering.

+ References

No definition available.

+ Details

Name:	us-gaap_ProFormaWeightedAverageSharesOutstandingDiluted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average number of shares (units) outstanding in the calculation of pro forma basic earnings per share (earnings per unit), which is commonly presented in initial public offerings based on the terms of the offering.

+ References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageBasicSharesOutstandingProForma
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAxis=bro_TwoThousandSixteenAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAxis=bro_TwoThousandEighteenAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: