Loans and Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses (Parenthetical) (Detail) - USD ($)		3 Months Ended				9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019		Jun. 30, 2020	Dec. 31, 2019		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Cumulative charges of loans and loan collateral process of foreclosure		$ 48,742,000	[1]	$ 53,539,000		$ 48,742,000	[1]	$ 53,539,000		$ 47,375,000	$ 52,711,000	[1]	$ 52,368,000	$ 49,495,000
Allowance for loan losses		90,510,000	[2],[3]	43,113,000	[2],[3]	90,510,000	[2],[3]	43,113,000	[2],[3]	$ 66,977,000	$ 46,093,000		$ 40,670,000	$ 36,395,000
Net charge-offs	[4]	16,216,000		5,894,000		28,814,000		30,133,000
Strategic Partnership [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses		0		0		0		0
Net charge-offs		0		$ 0		0		$ 0
Medallion Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Cumulative charges of loans and loan collateral process of foreclosure		$ 268,745,000				$ 268,745,000

[1] Includes financed sales of this collateral to third parties that are reported separately from the loan portfolio, and that are conducted by the Bank of $9,701 as of September 30, 2020 and $8,163 as of December 31, 2019.

[2] 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.    

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

[4] As of September 30, 2020, cumulative net charge-offs of loans and loan collateral in process of foreclosure in the medallion loan portfolio were $268,745, representing collection opportunities for the Company.