XML 48 R36.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Nature of Operations and Basis of Presentation - Additional Information (Detail) | 9 Months Ended
--- | ---
Sep. 30, 2017 Country Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Number of countries in which the company has operations | 34
Number of countries in which the company does business through a network of correspondent brokers and consultants | 150
Number of reportable segments | Segment | 3

X
- Definition Number of Countries in which the Company does Business through a Network of Correspondent Brokers and Consultants + References No definition available. + Details
Name: | ajg_NumberOfCountriesInWhichCompanyDoesBusinessThroughNetworkOfCorrespondentBrokersAndConsultants
Namespace Prefix: | ajg_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Countries in which the Company has Operations + References No definition available. + Details
Name: | ajg_NumberOfCountriesInWhichCompanyHasOperations
Namespace Prefix: | ajg_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration