Deferred Compensation Arrangement with Individual, Forfeited, Amount

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Grant Date Fair Value

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No definition available.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Measurement Input

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

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- Definition

Amount of cost for defined contribution plan.

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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No definition available.

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Percentage employer matches of the employee's percentage contribution matched.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

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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- Definition

An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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Compensation and Benefits - Additional Information (Details)			3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 01, 2018 USD ($)	Nov. 30, 2016	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation			$ 38,050,000	$ 6,120,000	$ 51,272,000	$ 18,484,000	$ 24,815,000	$ 193,299,000	$ 199,052,000
Deferred compensation			300,000	1,600,000	1,000,000	4,600,000	5,800,000	5,500,000	1,000.0
Deferred compensation, forfeited amount							$ 0	900,000	1,700,000
Employer matching contribution, percent of employees' gross pay							3.00%
Costs incurred for employee benefit plans			$ 1,200,000	$ 1,100,000	$ 3,800,000	3,500,000	$ 4,500,000	4,400,000	3,400,000
Termination cost						$ 5,400,000	$ 6,000,000.0
Deferred Profit Sharing \| Perella Weinberg Partners UK LLP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation								3,400,000	$ 800,000
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employer matching contribution, percent of match							10.00%
Various dates between January 1, 2022 and January 1, 2023 or earlier
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation								8,800,000
SLP Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years								4 years
Granted in period							$ 6,400,000	14,700,000	$ 4,600,000
Share-based payment arrangement, plan modification, incremental cost	$ 74,600,000
Equity-based compensation							24,800,000	$ 193,300,000	$ 199,100,000
Unrecognized compensation expense							$ 41,000,000.0
Weighted average period of unrecognized compensation cost related to unvested awards							2 years 8 months 15 days
SLP Awards \| Minimum \| Measurement Input, Discount Rate \| Valuation, Income Approach
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Measurement input	0.0990						0.038	0.036	0.0990	0.0980
SLP Awards \| Maximum \| Measurement Input, Discount Rate \| Valuation, Income Approach
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Measurement input	0.1080						0.112	0.121	0.1080	0.1110
SLP Awards \| Initial Tranche
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
SLP Awards \| Subsequent to Initial Tranche
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period							4 years