Related Parties - Payable to Employees and Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Related Party Transactions [Abstract]
Board Of Director Fees	$ 550	$ 567
Amount Due to U.K. Members	13,606	21,566
Amounts Due Pursuant To Tax Receivable Agreements (a)	9,891	9,570
Payable to Employees and Related Parties	24,047	31,703
Amounts Due Pursuant to Tax Receivable Agreements	$ 76,860	$ 84,952

Amount of payable due to an entity that is affiliated with the reporting entity by means of direct or indirect ownership. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a)(5))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(12)(b)(3))
-URI http://asc.fasb.org/extlink&oid=120401414&loc=d3e603758-122996

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