XML 91 R78.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Stock Option Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions |  |  |  | 12 Months Ended
--- | --- | --- | --- | ---
Mar. 16, 2021 | Mar. 12, 2020 | Mar. 14, 2019 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Stock Option Plans [Line Items] |  |  |  |  |  |
Compensation expense related to stock option grants |  |  |  | $ 17.5 | $ 13.6 | $ 14.0
Total intrinsic value of options exercised |  |  |  | 127.4 | $ 106.4 | $ 77.9
Total unrecognized compensation cost related to nonvested options |  |  |  | $ 47.1 |  |
Weighted average period, years |  |  |  | 4 years |  |
Black-Scholes Option Pricing Model [Member] |  |  |  |  |  |
Stock Option Plans [Line Items] |  |  |  |  |  |
Weighted average fair value per option for all options |  |  |  | $ 23.38 | $ 9.99 | $ 10.71
Long Term Incentive Plan [Member] |  |  |  |  |  |
Stock Option Plans [Line Items] |  |  |  |  |  |
Maximum number of shares available |  |  |  | 1,800,000 |  |
Shares available for grant |  |  |  | 9,500,000 |  |
Long Term Incentive Plan [Member] | Maximum [Member] |  |  |  |  |  |
Stock Option Plans [Line Items] |  |  |  |  |  |
Minimum exercise price of stock options, percent of fair market value of a share of common stock on the date of grant |  |  |  | 100.00% |  |
Maximum period for the exercise of stock options, years |  |  |  | 7 years | 7 years | 7 years
Long Term Incentive Plan [Member] | Minimum [Member] |  |  |  |  |  |
Stock Option Plans [Line Items] |  |  |  |  |  |
Period of service from grant date stock options awarded not subject to forfeiture |  |  |  | 2 years | 2 years | 2 years
Long Term Incentive Plan [Member] | Minimum [Member] | Executive Officer [Member] |  |  |  |  |  |
Stock Option Plans [Line Items] |  |  |  |  |  |
Minimum age of employee with not subject to award forfeiture on condition compliance |  |  |  | 55 years | 55 years | 55 years
2017 Long Term Incentive Plan [Member] |  |  |  |  |  |
Stock Option Plans [Line Items] |  |  |  |  |  |
Number Of Periods Options Expire |  |  |  | 7 years |  |
2017 Long Term Incentive Plan [Member] | Officer and Key Employees [Member] |  |  |  |  |  |
Stock Option Plans [Line Items] |  |  |  |  |  |
Shares available for grant | 1,640,000 | 1,590,740 | 1,283,300 |  |  |
Stock options granted, exercise percentage, on the third anniversary date of the grant | 34.00% | 34.00% | 34.00% |  |  |
Stock options granted, exercise percentage, on the fourth anniversary date of the grant | 33.00% | 33.00% | 33.00% |  |  |
Stock options granted, exercise percentage, on the fifth anniversary date of the grant | 33.00% | 33.00% | 33.00% |  |  |

X
- Definition Age Of Employee No Longer Subject To Award Forfeiture On Condition Compliance + References No definition available. + Details
Name: | ajg_AgeOfEmployeeNoLongerSubjectToAwardForfeitureOnConditionCompliance
Namespace Prefix: | ajg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Exercise Price Of Stock Options Percent Of Fair Market Value Of Share Of Common Stock On Date Of Grant. + References No definition available. + Details
Name: | ajg_ExercisePriceOfStockOptionsPercentOfFairMarketValueOfShareOfCommonStockOnDateOfGrant
Namespace Prefix: | ajg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of years options expire. + References No definition available. + Details
Name: | ajg_NumberOfPeriodsOptionsExpire
Namespace Prefix: | ajg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period for options to expire from date of grant. + References No definition available. + Details
Name: | ajg_PeriodForOptionsToExpireFromDateOfGrant
Namespace Prefix: | ajg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period Of Service From Grant Date Stock Options Awarded Not Subject To Forfeiture + References No definition available. + Details
Name: | ajg_PeriodOfServiceFromGrantDateStockOptionsAwardedNotSubjectToForfeiture
Namespace Prefix: | ajg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share-based compensation arrangement by share based payment award options exercised in period intrinsic value. + References No definition available. + Details
Name: | ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue
Namespace Prefix: | ajg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Share based compensation arrangement by share based payment award options grants in period exercise percentage year one. + References No definition available. + Details
Name: | ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePercentageYearOne
Namespace Prefix: | ajg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based compensation arrangement by share based payment award options grants in period exercise percentage year three. + References No definition available. + Details
Name: | ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePercentageYearThree
Namespace Prefix: | ajg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based compensation arrangement by share based payment award options grants in period exercise percentage year two. + References No definition available. + Details
Name: | ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePercentageYearTwo
Namespace Prefix: | ajg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Stock Option Plans [Line Items] + References No definition available. + Details
Name: | ajg_StockOptionPlansLineItems
Namespace Prefix: | ajg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted Average Period + References No definition available. + Details
Name: | ajg_WeightedAveragePeriod
Namespace Prefix: | ajg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cost not yet recognized for nonvested award under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Value, after forfeiture, of shares granted under share-based payment arrangement. Excludes employee stock ownership plan (ESOP). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 30 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=121321822&loc=d3e3913-113898 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 30 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121323062&loc=d3e15009-113911 + Details
Name: | us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=ajg_BlackScholesOptionPricingModelMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=ajg_LongTermIncentivePlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_TitleOfIndividualAxis=srt_ExecutiveOfficerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=ajg_TwoThousandSeventeenLongTermincentivePlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_TitleOfIndividualAxis=srt_OfficerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |