Organization and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Jul. 30, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
Business Acquisition [Line Items]
Operating lease ROU assets		$ 134,342		$ 165,969
Operating lease liabilities		163,887		190,207
Assets		(5,415,607)		(3,953,242)
Noncontrolling interest in subsidiaries		(685,165)	$ (794,360)	(811,297)	$ (773,245)	$ (748,953)		$ (729,106)
Retained deficit		1,244,718		1,280,828
Futures Exchange Group
Business Acquisition [Line Items]
Payments to acquire businesses	$ 4,900
Cumulative Effect, Period of Adoption, Adjustment
Business Acquisition [Line Items]
Operating lease ROU assets									$ 192,400
Operating lease liabilities									$ 206,000
Noncontrolling interest in subsidiaries								1,300
Assets | Cumulative Effect, Period of Adoption, Adjustment
Business Acquisition [Line Items]
Assets							$ 1,900
Tax effect impact for increase or decrease to the liability							600
Noncontrolling Interest in Subsidiaries
Business Acquisition [Line Items]
Noncontrolling interest in subsidiaries		(54,261)	(64,028)	(57,061)	(58,536)	(55,849)		(48,976)
Noncontrolling Interest in Subsidiaries | Cumulative Effect, Period of Adoption, Adjustment
Business Acquisition [Line Items]
Noncontrolling interest in subsidiaries							600	417
Tax effect impact for increase or decrease to the liability							200
Retained Deficit
Business Acquisition [Line Items]
Noncontrolling interest in subsidiaries		$ 1,244,718	$ 1,229,498	$ 1,280,828	$ 1,273,173	$ 1,278,419		1,264,567
Retained Deficit | Cumulative Effect, Period of Adoption, Adjustment
Business Acquisition [Line Items]
Noncontrolling interest in subsidiaries								$ 883
Retained deficit							1,300
Tax effect impact for increase or decrease to the liability							$ 400