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Business Acquisitions Purchase Price Allocation Goodwill Amount

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Business Combination ,Aggregate Earnout Obligation, Maximum

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Business Combination Aggregate Earnout Obligation Recorded Maximum

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Expected business consideration to be transferred.

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Expiration lists

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Fair Value Inputs, Attrition Rate

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Number of employees.

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Number of offices.

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Number of states.

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

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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.

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

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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For transactions that are recognized separately from the acquisition of assets and assumptions of liabilities in the business combination, such as related to pre-existing relationships with the acquiree, this element represents the disclosure of the amount of acquisition related costs which have been expensed.

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Amount of deferred tax liability attributable to taxable temporary differences.

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Gross carrying amount before accumulated amortization as of the balance sheet date of payments made to third parties in exchange for their agreement not to engage in specified competitive practices in specified geographic territories for a specified period of time.

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Business Combinations - Additional Information (Detail) $ in Millions			3 Months Ended		9 Months Ended		261 Months Ended
	Oct. 24, 2023 USD ($) Office State	Apr. 03, 2023 Employee	Sep. 30, 2023 USD ($) Entity	Sep. 30, 2022 USD ($) Entity	Sep. 30, 2023 USD ($) Entity	Sep. 30, 2022 USD ($) Entity	Sep. 30, 2023 USD ($) Entity	Sep. 19, 2023 USD ($)
Business Acquisition [Line Items]
Accretion of the discount on acquisition			$ 17.9	$ 19.4	$ 57.5	$ 42.8
Income (expense) related to net adjustments to estimated fair value of liability for earnout obligations			$ 20.4	$ 35.6	$ (8.8)	$ 71.9
Number of companies acquired \| Entity			20	27	59	70	687
Aggregate amount of maximum earnout obligations related to acquisitions					$ 1,915.7
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet					899.0
Aggregate amount of earnout obligation expected settlement in cash or stock at option			$ 486.6		486.6		$ 486.6
Aggregate amount of earnout obligation expected settlement in cash			412.4		412.4		412.4
Goodwill			957.9		957.9		957.9
Expiration lists			667.9		667.9		667.9
Non-compete agreements			15.6		15.6		15.6
Trade names			4.2		4.2		4.2
Total revenues			2,500.4	$ 2,159.0	7,781.9	$ 6,877.5
Brokerage Management [Member]
Business Acquisition [Line Items]
Goodwill			957.9		957.9		957.9
Expiration lists			667.9		667.9		667.9
Non-compete agreements			15.6		15.6		15.6
Trade names			4.2		4.2		4.2
Brokerage and Risk Management [Member]
Business Acquisition [Line Items]
Write-off of amortizable intangible assets					3.3	$ 0.4
Brokerage [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes			441.4		441.4		441.4
Brokerage [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes			12.4		12.4		12.4
Brokerage [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes			$ 2.9		$ 2.9		$ 2.9
Minimum [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			2 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		2 years
Minimum [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			2 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		15 years
Maximum [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			6 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		15 years
2023 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input			0.05		0.05		0.05
2023 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input			0.20		0.20		0.20
2023 Acquisitions [Member] \| Valuation, Income Approach \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input			0.08		0.08		0.08
2023 Acquisitions [Member] \| Valuation, Income Approach \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input			0.09		0.09		0.09
2022 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		0.03
2022 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input			0.05		0.05		0.05
2022 Acquisitions [Member] \| Valuation, Income Approach \| Minimum [Member]
Business Acquisition [Line Items]
Attrition rate					5.00%
2022 Acquisitions [Member] \| Valuation, Income Approach \| Maximum [Member]
Business Acquisition [Line Items]
Attrition rate					25.50%
2022 Acquisitions [Member] \| Valuation, Income Approach \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input			0.09	0.09	0.09	0.09	0.09
2022 Acquisitions [Member] \| Valuation, Income Approach \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input			0.11	0.11	0.11	0.11	0.11
Business Acquisition [Member]
Business Acquisition [Line Items]
Annualized revenue of business acquisitions					$ 475.3
Total revenues					223.3
Net earnings					(1.9)
Net earnings before interest, income taxes, depreciation, amortization and change in estimated acquisition earnout payables					43.5
Business Acquisition [Member] \| Brokerage [Member]
Business Acquisition [Line Items]
Expiration lists			$ 667.9		667.9		$ 667.9
Non-compete agreements			15.6		15.6		15.6
Trade names			4.2		4.2		4.2
Deferred tax liability			$ 113.5		$ 113.5		$ 113.5
Cadence Insurance [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Consideration amount	$ 749.0
Consideration amount net of discounted tax benefit	$ 155.0
Number of offices operating \| Office	34
Number of states operating \| State	9
BCHR Holdings, L.P [Member]
Business Acquisition [Line Items]
Number of employees \| Employee		2,300
Number of employees with credentialed actuaries \| Employee		220
Eastern Insurance Group, LLC [Member]
Business Acquisition [Line Items]
Expected business consideration to be transferred								$ 510.0