Loans and Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended	9 Months Ended
		Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - beginning balance		$ 40,670		$ 21,425		$ 36,395
Total charge-offs		(9,209)		(11,941)	$ (23,428)	(39,248)
Total recoveries		3,315		1,795	4,131	9,115
Net charge-offs	[1]	(5,894)		(10,146)	(19,297)	(30,133)
Provision for loan losses		8,337		18,205	48,781	36,851		$ 48,781	[2]
Allowance for loan losses - ending balance		43,113	[3]	29,484	29,484	43,113	[3]	$ 29,484
Recreation [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - beginning balance						6,856
Total charge-offs		(5,444)		(4,825)	(9,471)	(16,366)
Total recoveries		1,955		1,318	3,217	5,513
Allowance for loan losses - ending balance		15,927				15,927
Home Improvement [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - beginning balance						1,796
Total charge-offs		(568)		(659)	(1,220)	(1,655)
Total recoveries		517		367	606	1,360
Allowance for loan losses - ending balance		2,235				2,235
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total charge-offs		(819)				(819)
Total recoveries					4
Medallion [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - beginning balance						27,743
Total charge-offs		(2,378)		(6,457)	(12,737)	(20,408)
Total recoveries		843		$ 110	$ 304	2,242
Allowance for loan losses - ending balance		$ 24,951				$ 24,951

[1] As of September 30, 2019, cumulative net charge-offs of loans and loans in process of foreclosure in the medallion portfolio were $242,889, representing collection opportunities for the Company.

[2] Results include the six months ended September 30, 2018 under Bank Holding Company Accounting and the three months ended March 31, 2018 under Investment Company Accounting.

[3] Includes $4,608 of a general reserve for the Company, for current and performing medallion loans under 90 days past due, as an additional buffer against future losses, representing 11% of the total allowance, and 3.56% of the medallion loans under 90 days past due as of September 30, 2019. This figure excludes $17,351 of a general reserve on loans at the Bank, which was netted against loan balances at consolidation on April 2, 2018. Subsequent to April 2, 2018, the Bank recorded general reserves of $6,032.