Receivables - Additional Information (Detail) - USD ($)	Sep. 30, 2020		Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	[1]	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-bearing financing fee receivables	$ 82,179,000			$ 77,052,000
Allowance for doubtful accounts receivables	38,250,000	[1]	$ 40,959,000	27,130,000	$ 31,288,000		$ 33,535,000	$ 40,164,000
Aggregate carrying amount of non-interest bearing receivables	492,919,000			586,086,000
Financing Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts receivables	$ 0			$ 0

[1] The allowance for doubtful accounts balances are substantially all related to M&A and Restructuring fee receivables that include recoverable expense receivables.