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Business Combinations - Additional Information (Detail) $ in Millions |  |  |  |  |  | 3 Months Ended | 279 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 04, 2025 USD ($) Employee Office | Jan. 07, 2025 USD ($) | Dec. 19, 2024 USD ($) | Dec. 11, 2024 USD ($) | Dec. 07, 2024 USD ($) | Mar. 31, 2025 USD ($) Entity | Mar. 31, 2024 USD ($) Entity | Mar. 31, 2025 USD ($) Entity
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Cash raised through follow-on common stock offering |  |  |  |  |  | $ 1,334.8 | $ 52.0 |
Accretion of the discount on acquisition |  |  |  |  |  | 13.0 | 18.8 |
Income (expense) related to net adjustments to estimated fair value of liability for earnout obligations |  |  |  |  |  | $ 2.8 | $ 34.9 |
Number of companies acquired | Entity |  |  |  |  |  | 28 | 37 | 761
Aggregate amount of maximum earnout obligations related to acquisitions |  |  |  |  |  | $ 2,154.0 |  |
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet |  |  |  |  |  | 1,368.0 |  |
Aggregate amount of earnout obligation expected settlement in cash or stock at option |  |  |  |  |  | 576.3 |  | $ 576.3
Aggregate amount of earnout obligation expected settlement in cash |  |  |  |  |  | 791.7 |  | 791.7
Goodwill |  |  |  |  |  | 258.0 |  | 258.0
Expiration lists |  |  |  |  |  | 200.8 |  | 200.8
Non-compete agreements |  |  |  |  |  | 16.9 |  | 16.9
Net increase to goodwill |  |  |  |  |  | 53.8 |  |
Total revenues |  |  |  |  |  | 3,741.1 | $ 3,285.7 |
Brokerage [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Net increase to goodwill |  |  |  |  |  | 53.8 |  |
Write-off of amortizable intangible assets |  |  |  |  |  | 40.6 |  |
Brokerage [Member] | Expiration Lists [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Business acquisition not deductible for income tax purposes |  |  |  |  |  | 163.9 |  | 163.9
Brokerage [Member] | Non-Compete Agreements [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Business acquisition not deductible for income tax purposes |  |  |  |  |  | 16.3 |  | 16.3
Insurance Brokerage Management Services [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  | 258.0 |  | 258.0
Expiration lists |  |  |  |  |  | 200.8 |  | 200.8
Non-compete agreements |  |  |  |  |  | $ 16.9 |  | $ 16.9
Minimum [Member] | Expiration Lists [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Estimated useful lives of intangibles assets, years |  |  |  |  |  | 2 years |  | 2 years
Minimum [Member] | Non-Compete Agreements [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Estimated useful lives of intangibles assets, years |  |  |  |  |  | 2 years |  | 2 years
Minimum [Member] | Trade Names [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Estimated useful lives of intangibles assets, years |  |  |  |  |  | 2 years |  | 2 years
Maximum [Member] | Expiration Lists [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Estimated useful lives of intangibles assets, years |  |  |  |  |  | 15 years |  | 15 years
Maximum [Member] | Non-Compete Agreements [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Estimated useful lives of intangibles assets, years |  |  |  |  |  | 6 years |  | 6 years
Maximum [Member] | Trade Names [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Estimated useful lives of intangibles assets, years |  |  |  |  |  | 15 years |  | 15 years
AssuredPartners, Inc [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Gross consideration |  |  |  |  | $ 13,450.0 |  |  |
Cash raised through follow-on common stock offering |  |  |  | $ 8,500.0 |  |  |  |
AssuredPartners, Inc [Member] | Over-Allotment Option [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Cash raised through follow-on common stock offering |  | $ 1,280.0 |  |  |  |  |  |
AssuredPartners, Inc [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Cash borrowed from senior notes |  |  | $ 5,000.0 |  |  |  |  |
Woodruff Sawyer & Co. [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Gross consideration | $ 1,200.0 |  |  |  |  |  |  |
Number of employees | Employee | 600 |  |  |  |  |  |  |
Woodruff Sawyer & Co. [Member] | Unites States [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Number of offices operating | Office | 14 |  |  |  |  |  |  |
Woodruff Sawyer & Co. [Member] | United Kingdom [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Number of offices operating | Office | 1 |  |  |  |  |  |  |
2025 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Discount Rate [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Measurement input |  |  |  |  |  | 0.05 |  | 0.05
2025 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Discount Rate [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Measurement input |  |  |  |  |  | 0.175 |  | 0.175
2025 Acquisitions [Member] | Valuation, Income Approach | Measurement Input, Discount Rate [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Measurement input |  |  |  |  |  | 0.09 |  | 0.09
2025 Acquisitions [Member] | Valuation, Income Approach | Measurement Input, Long-term Revenue Growth Rate [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Measurement input |  |  |  |  |  | 0.11 |  | 0.11
2024 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Measurement input |  |  |  |  |  | 0.03 |  | 0.03
2024 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Measurement input |  |  |  |  |  | 0.041 |  | 0.041
2024 Acquisitions [Member] | Valuation, Income Approach | Minimum [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Attrition rate |  |  |  |  |  | 5.00% |  |
2024 Acquisitions [Member] | Valuation, Income Approach | Maximum [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Attrition rate |  |  |  |  |  | 12.00% |  |
Business Acquisition [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Annualized revenue of business acquisitions |  |  |  |  |  | $ 100.9 |  |
Total revenues |  |  |  |  |  | 14.3 |  |
Net earnings |  |  |  |  |  | (1.3) |  |
Net earnings before interest, income taxes, depreciation, amortization and change in estimated acquisition earnout payables |  |  |  |  |  | 2.9 |  |
Business Acquisition [Member] | Brokerage [Member] |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Expiration lists |  |  |  |  |  | 200.8 |  | $ 200.8
Non-compete agreements |  |  |  |  |  | 16.9 |  | 16.9
Deferred tax liability |  |  |  |  |  | $ 47.2 |  | $ 47.2

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