Loans and Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2020 USD ($) TDR		Sep. 30, 2019 USD ($) TDR		Sep. 30, 2020 USD ($) TDR		Sep. 30, 2019 USD ($) TDR		Sep. 30, 2020 USD ($) TDR		Sep. 30, 2019 USD ($) TDR		Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Weighted average loan-to-value ratio	316.00%		202.00%		316.00%		202.00%		316.00%		202.00%			190.00%
Allowance for loan loss	$ 90,510,000	[1],[2]	$ 43,113,000	[1],[2]	$ 90,510,000	[1],[2]	$ 43,113,000	[1],[2]	$ 90,510,000	[1],[2]	$ 43,113,000	[1],[2]	$ 66,977,000	$ 46,093,000	$ 40,670,000	$ 36,395,000
Medallion [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans modified as TDRs defaulted | TDR	3		1		33		10
Allowance for loan loss	$ 57,777,000				$ 57,777,000				57,777,000					25,410,000
Recreation [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans modified as TDRs defaulted | TDR	18		40		57		276
Allowance for loan loss	$ 27,982,000				$ 27,982,000				$ 27,982,000					$ 18,075,000
Troubled Debt Restructuring Defaulted [Member] | Medallion [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans modified as TDRs defaulted | TDR									69		3
TDR investment value	29,296,000		$ 812,000		29,296,000		$ 812,000		$ 29,296,000		$ 812,000
Allowance for loan loss	20,420,000		365,000		$ 20,420,000		$ 365,000		20,420,000		365,000
Troubled Debt Restructuring Defaulted [Member] | Recreation [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans modified as TDRs defaulted | TDR					56		191
TDR investment value	558,000		1,727,000		$ 558,000		$ 1,727,000		558,000		1,727,000
Allowance for loan loss	$ 19,000		$ 66,000		$ 19,000		$ 66,000		$ 19,000		$ 66,000

[1] As of September 30, 2020, the general reserves previously recorded for the Company’s medallion loan portfolio had been reversed as all loans had been deemed impaired and written down to collateral value.    

[2] As of September 30, 2020, there was no allowance for loan losses and net charge-offs related to the strategic partnership loans.