XML 55 R42.htm IDEA: XBRL DOCUMENT
v3.20.2

Business Combinations - Acquisition Method for Recording Business Combinations (Detail) shares in Thousands | 9 Months Ended
--- | ---
Sep. 30, 2020 USD ($) shares
Business Acquisition [Line Items] |
Common Shares Issued | shares | 1,186
Common Shares Issued | $ 119,300,000
Cash Paid | 156,400,000
Accrued Liability | 1,800,000
Escrow Deposited | 11,600,000
Recorded Earnout Payable | 160,700,000
Total Recorded Purchase Price | 449,800,000
Maximum Potential Earnout Payable | $ 275,700,000
Capsicum Reinsurance Brokers LLP (CRB) [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 584
Common Shares Issued | $ 62,900,000
Cash Paid | 64,500,000
Recorded Earnout Payable | 129,900,000
Total Recorded Purchase Price | 257,300,000
Maximum Potential Earnout Payable | 209,100,000
Hanover Excess and Surplus, Inc and Hanover Premium Finance, Inc (HES) [Member] |
Business Acquisition [Line Items] |
Cash Paid | 30,100,000
Escrow Deposited | 3,000,000.0
Total Recorded Purchase Price | 33,100,000
Maximum Potential Earnout Payable | $ 9,300,000
CRES Insurance Services, LLC [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 288
Common Shares Issued | $ 28,500,000
Cash Paid | 1,500,000
Escrow Deposited | 1,000,000.0
Recorded Earnout Payable | 5,500,000
Total Recorded Purchase Price | 36,500,000
Maximum Potential Earnout Payable | $ 7,300,000
Fourteen Other Acquisitions [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 314
Common Shares Issued | $ 27,900,000
Cash Paid | 60,300,000
Accrued Liability | 1,800,000
Escrow Deposited | 7,600,000
Recorded Earnout Payable | 25,300,000
Total Recorded Purchase Price | 122,900,000
Maximum Potential Earnout Payable | $ 50,000,000.0

X
- Definition Business Acquisition Cost Of Acquired Entity Purchase Price Net + References No definition available. + Details
Name: | ajg_BusinessAcquisitionCostOfAcquiredEntityPurchasePriceNet
Namespace Prefix: | ajg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business combination recognized identifiable assets acquired and liabilities accrued liability. + References No definition available. + Details
Name: | ajg_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAccruedLiability
Namespace Prefix: | ajg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Maximum Potential Earnout Payable + References No definition available. + Details
Name: | ajg_MaximumPotentialEarnoutPayable
Namespace Prefix: | ajg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Recorded Earnout Payable + References No definition available. + Details
Name: | ajg_RecordedEarnOutPayable
Namespace Prefix: | ajg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of shares of equity interests issued or issuable to acquire entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b)(4) -URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479 + Details
Name: | us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- 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_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477 + Details
Name: | us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy. + 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 210.9-03.10) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
Name: | us-gaap_EscrowDeposit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireBusinessesGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=ajg_CapsicumReinsuranceBrokersLLPMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=ajg_HanoverExcessAndSurplusIncAndHanoverPremiumFinanceIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=ajg_CRESInsuranceServicesLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=ajg_OtherAcquisitionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |