Loans and Allowance for Loan Losses - Summary of Allowance for Loan Losses by Type (Detail) - USD ($) $ in Thousands	Sep. 30, 2020		Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	[1],[2]	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 90,510	[1],[2]	$ 66,977	$ 46,093	$ 43,113		$ 40,670	$ 36,395
Percentage of Allowance	100.00%			100.00%
Allowance as a Percent of Loan Category	7.07%			3.97%
Recreation [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 27,982			$ 18,075
Percentage of Allowance	31.00%			39.00%
Allowance as a Percent of Loan Category	3.48%			2.53%
Home Improvement [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 4,751			$ 2,608
Percentage of Allowance	5.00%			6.00%
Allowance as a Percent of Loan Category	1.51%			1.05%
Medallion [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 57,777			$ 25,410
Percentage of Allowance	64.00%			55.00%
Allowance as a Percent of Loan Category	63.28%			19.48%

[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.