Business Acquisition Purchase Price Allocation Goodwill Not Expected Tax Deductible Amount

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- Definition

Business Acquisitions Purchase Price Allocation Goodwill Amount

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- Definition

Business Combination ,Aggregate Earnout Obligation, Maximum

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- Definition

Business Combination Aggregate Earnout Obligation Recorded Maximum

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Business Combination, Annualize Revenue

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- Definition

Expiration lists

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- Definition

Fair Value Inputs, Attrition Rate

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No definition available.

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- Definition

Value of input used to measure alternative investment.

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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.

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No definition available.

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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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- Definition

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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- Definition

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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- Definition

Amount of deferred tax liability attributable to taxable temporary differences.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Gross carrying amount before accumulated amortization as of the balance sheet date of the rights acquired through registration of a trade name to gain or protect exclusive use thereof for a reasonably expected period of economic benefit.

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The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of a finite-lived intangible asset to fair value.

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The number of businesses acquired by the entity during the period.

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Business Combinations - Additional Information (Detail)	3 Months Ended		9 Months Ended		225 Months Ended
Business Combinations - Additional Information (Detail)	Sep. 30, 2020 USD ($) Entity	Sep. 30, 2019 USD ($) Entity	Sep. 30, 2020 USD ($) Entity	Sep. 30, 2019 USD ($) Entity	Sep. 30, 2020 USD ($) Entity
Business Acquisition [Line Items]
Accretion of the discount on acquisition	$ 5,900,000	$ 7,100,000	$ 24,300,000	$ 18,500,000
Income (expense) related to net adjustments to estimated fair value of liability for earnout obligations	$ (14,200,000)	$ 1,400,000	$ 77,400,000	$ 6,500,000
Number of companies acquired \| Entity	55	29	126	86	573
Aggregate amount of maximum earnout obligations related to acquisitions			$ 1,026,100,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet			502,500,000
Goodwill	$ 200,700,000		200,700,000		$ 200,700,000
Expiration lists	229,200,000		229,200,000		229,200,000
Non-compete agreements	3,600,000		3,600,000		3,600,000
Trade names	5,000,000.0		5,000,000.0		5,000,000.0
Total revenues	1,850,600,000	$ 1,839,200,000	5,315,700,000	$ 5,515,900,000
Brokerage and Risk Management [Member]
Business Acquisition [Line Items]
Goodwill	200,700,000		200,700,000		200,700,000
Expiration lists	229,200,000		229,200,000		229,200,000
Non-compete agreements	3,600,000		3,600,000		3,600,000
Trade names	5,000,000.0		5,000,000.0		5,000,000.0
Brokerage [Member]
Business Acquisition [Line Items]
Impairment wrote off of amortizable assets	3,700,000		49,700,000	$ 0
Brokerage [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes	8,800,000		8,800,000		8,800,000
Brokerage [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes	100,000		100,000		100,000
Brokerage [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes	$ 0		$ 0		$ 0
Minimum [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			2 years
Minimum [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			2 years
Minimum [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			2 years
Maximum [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			15 years
Maximum [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			6 years
Maximum [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			15 years
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input	2.5		2.5		2.5
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input	15.0		15.0		15.0
2020 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input	6.0		6.0		6.0
2020 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input	9.0		9.0		9.0
2018 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input	1.5	1.5	1.5	1.5	1.5
2018 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input	4.1	4.1	4.1	4.1	4.1
2018 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input	9.0	9.0	9.0	9.0	9.0
2018 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input	13.5	13.5	13.5	13.5	13.5
2017 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Attrition rate			5.00%	5.00%
2017 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Attrition rate			15.70%	15.70%
Business Acquisition [Member]
Business Acquisition [Line Items]
Trade names	$ 5,000,000.0		$ 5,000,000.0		$ 5,000,000.0
Annualized revenue of business acquisitions				$ 151,200,000
Total revenues				30,400,000
Net earnings				$ 4,300,000
Business Acquisition [Member] \| Brokerage [Member]
Business Acquisition [Line Items]
Expiration lists	229,200,000		229,200,000		229,200,000
Non-compete agreements	3,600,000		3,600,000		3,600,000
Deferred tax liability	$ 2,500,000		$ 2,500,000		$ 2,500,000