This element represents the amount of recognized equity-based issuances to employees during the period.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Company's directors have elected to defer percentage of their compensation in the form of phantom shares of Class A common stock under director plan.

+ References

No definition available.

+ Details

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- Definition

Number of shares issued pursuant to the terms of a deferred compensation arrangement.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

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

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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

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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.

+ References

No definition available.

+ Details

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

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- Definition

Number of options vested.

+ References

No definition available.

+ Details

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- Definition

Number of shares issued which are neither cancelled nor held in the treasury.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Number of shares of capital stock issued (purchased by employees) in connection with an employee stock ownership plan.

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- Definition

Value of stock issued in lieu of cash for services contributed to the entity. Value of the stock issued includes, but is not limited to, services contributed by vendors and founders.

+ References

No definition available.

+ Details

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Compensation and Benefits - Narrative (Details) - USD ($) $ in Thousands			3 Months Ended						9 Months Ended		12 Months Ended
	May 01, 2020	Jan. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Compensation Arrangements [Line Items]
Deferred compensation liability			$ 2,940						$ 2,940		$ 3,600
Unrecorded compensation expense			$ 34,900						$ 34,900		$ 39,400
Common Class B
Compensation Arrangements [Line Items]
Delayed Exchange Class B units issued (in shares)			20,581	96,600	430,955	5,501	237	10,399	548,136	16,137
Delayed Exchange Class B units issued			$ 100						$ 2,300	$ 100
Common Class B \| Maximum
Compensation Arrangements [Line Items]
Delayed Exchange Class B units issued						$ 100
Phantom Shares of Class A common stock \| Director Plan
Compensation Arrangements [Line Items]
Deferred compensation percentage of compensation directors elected									100.00%
Shares forfeited									49,673
Shares outstanding (in shares)			493,207						493,207		455,028
Distributions made under Director Plan (in shares)			0			0			0	0
Equity Incentive Plan 2006
Compensation Arrangements [Line Items]
Cash compensation paid in the form of equity											$ 3,800
Equity Incentive Plan 2006 \| Options To Purchase Delayed Exchange Class B Units
Compensation Arrangements [Line Items]
Grants in period (in shares)	42,735								0	314,960
Equity Incentive Plan 2006 \| Options to Purchase Shares of Class A Common Stock
Compensation Arrangements [Line Items]
Grants in period (in shares)	42,735	42,735
Equity Incentive Plan 2006 \| Delayed Exchange Unit
Compensation Arrangements [Line Items]
Grants in period (in shares)	16,806	620,543
Equity Incentive Plan 2006 \| Restricted Shares of Class A Common Stock
Compensation Arrangements [Line Items]
Grants in period (in shares)	16,806	16,806
2007 Equity Incentive Plan \| Contingent Options to Purchase Shares of Class A Common Stock
Compensation Arrangements [Line Items]
Number of shares vested during period			0			0			0	0
2007 Equity Incentive Plan \| Options to Purchase Shares of Class A Common Stock
Compensation Arrangements [Line Items]
Grants in period (in shares)									146,804	0
Vesting period for units (in years)	5 years
2007 Equity Incentive Plan \| Restricted Shares of Class A Common Stock
Compensation Arrangements [Line Items]
Grants in period (in shares)									16,806	0
Vesting period for units (in years)	4 years
Bonus plan
Compensation Arrangements [Line Items]
Vesting period for units (in years)									4 years
Bonus plan \| Common Class B
Compensation Arrangements [Line Items]
Delayed Exchange Class B units issued (in shares)									10,971
Delayed Exchange Class B units issued									$ 100