Segment Reporting - Schedule of Segment Data (Detail) - USD ($) $ in Thousands		3 Months Ended																					9 Months Ended		12 Months Ended
		Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018	[3]	Jun. 30, 2018	[3]	Mar. 31, 2018	[3]	Dec. 31, 2017	[3]	Sep. 30, 2017	[3]	Jun. 30, 2017	[3]	Mar. 31, 2017	[3]	Dec. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Segment Reporting Disclosure [Line Items]
Total interest income																							$ 96,803		$ 132,562
Total interest expense																							24,816		35,045		$ 28,367	[1],[2]
Net interest income/net investment income		$ 26,587		$ 25,415	$ 23,194	$ 22,321	$ 23,003	[3]	$ 24,265		$ 24,719		$ 482		$ 6,020		$ 5,567		$ 3,787		$ 4,250		71,987		97,517		72,469	[2]
Provision for loan losses																							59,008	[4]	47,386		59,008	[2]
Net interest income (loss) after loss provision																							12,979		50,131		13,461	[2]
Sponsorship and race winnings																							14,368		18,742		14,368	[2]
Race team related expenses																							(7,121)		(8,996)		(7,121)	[2]
Other income (expense), net																							(27,382)		(57,540)
Income (loss) before income taxes/net investment loss before taxes		2,076		7,600	(8,478)	1,139	14,712	[3]	(3,963)		(17,905)		(3,566)		(2,903)		(2,490)		(1,293)		(435)		(7,156)		2,337		(10,722)	[2],[5]
Income tax (provision) benefit																							(709)		(341)		(69)		$ 36,226
Net income (loss) after taxes/net increase (decrease) on net assets resulting from operations		(191)		$ 7,435	$ (6,643)	$ 1,395	9,865	[3]	$ (3,846)		$ (13,884)		$ (14,874)		$ 3,345		$ 619		$ (4,797)		$ 1,111		(7,865)		1,996		(22,739)	[2]
Balance Sheet Data
Total loans net		1,114,762					981,487																981,487		1,114,762		981,487
Total assets		1,541,667					1,381,846																1,381,846		1,541,667		1,381,846
Total funds borrowed		1,169,593	[6]				1,062,028																$ 1,062,028		$ 1,169,593	[6]	1,062,028
Selected Financial Ratios
Return on average assets																							(0.90%)		(0.12%)
Return on average equity																							(4.62%)		(0.59%)
Interest yield																							10.98%		11.75%
Net interest margin																							8.19%		8.64%
Reserve coverage																							3.58%		3.97%
Delinquency status	[7]																						2.14%		0.76%
Charge-off ratio																							2.73%		3.60%
RPAC [Member]
Segment Reporting Disclosure [Line Items]
Total interest expense																							$ 121		$ 159
Net interest income/net investment income																							(121)		(159)
Net interest income (loss) after loss provision																							(121)		(159)
Sponsorship and race winnings																							14,368		18,742
Race team related expenses																							(7,121)		(8,996)
Other income (expense), net																							(11,476)		(6,942)
Income (loss) before income taxes/net investment loss before taxes																							(4,350)		2,645
Income tax (provision) benefit																							1,108		(329)
Net income (loss) after taxes/net increase (decrease) on net assets resulting from operations																							(3,242)		2,316
Balance Sheet Data
Total assets		31,538					29,925																29,925		31,538		29,925
Total funds borrowed		7,794					7,649																$ 7,649		$ 7,794		7,649
Selected Financial Ratios
Return on average assets																							(11.69%)		7.28%
Return on average equity																									(96.37%)
Operating Segments [Member] | Consumer Lending [Member] | Recreation [Member]
Segment Reporting Disclosure [Line Items]
Total interest income																							$ 68,870		$ 99,463
Total interest expense																							6,986		13,304
Net interest income/net investment income																							61,884		86,159
Provision for loan losses																							15,118		28,638
Net interest income (loss) after loss provision																							46,766		57,521
Other income (expense), net																							(14,242)		(23,490)
Income (loss) before income taxes/net investment loss before taxes																							32,524		34,031
Income tax (provision) benefit																							(8,579)		(8,813)
Net income (loss) after taxes/net increase (decrease) on net assets resulting from operations																							23,945		25,218
Balance Sheet Data
Total loans net		695,257					580,182																580,182		695,257		580,182
Total assets		707,377					590,746																590,746		707,377		590,746
Total funds borrowed		563,805					434,527																$ 434,527		$ 563,805		434,527
Selected Financial Ratios
Return on average assets																							5.48%		3.84%
Return on average equity																							22.60%		17.19%
Interest yield																							15.78%		15.39%
Net interest margin																							14.18%		13.33%
Reserve coverage																							1.17%		2.53%
Delinquency status	[7]																						0.73%		0.84%
Charge-off ratio																							1.89%		2.69%
Operating Segments [Member] | Consumer Lending [Member] | Home Improvement [Member]
Segment Reporting Disclosure [Line Items]
Total interest income																							$ 12,799		$ 19,943
Total interest expense																							2,290		4,757
Net interest income/net investment income																							10,509		15,186
Provision for loan losses																							2,453		1,598
Net interest income (loss) after loss provision																							8,056		13,588
Other income (expense), net																							(3,093)		(7,520)
Income (loss) before income taxes/net investment loss before taxes																							4,963		6,068
Income tax (provision) benefit																							(1,319)		(1,572)
Net income (loss) after taxes/net increase (decrease) on net assets resulting from operations																							3,644		4,496
Balance Sheet Data
Total loans net		244,716					181,359																181,359		244,716		181,359
Total assets		252,704					188,892																188,892		252,704		188,892
Total funds borrowed		201,605					143,815																$ 143,815		$ 201,605		143,815
Selected Financial Ratios
Return on average assets																							2.56%		2.20%
Return on average equity																							11.30%		10.22%
Interest yield																							9.06%		9.50%
Net interest margin																							7.44%		7.24%
Reserve coverage																							0.98%		1.05%
Delinquency status	[7]																						0.07%		0.07%
Charge-off ratio																							0.46%		0.37%
Operating Segments [Member] | Commercial Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income																							$ 7,076		$ 7,183
Total interest expense																							1,502		2,833
Net interest income/net investment income																							5,574		4,350
Provision for loan losses																									364
Net interest income (loss) after loss provision																							5,574		3,986
Other income (expense), net																							(1,824)		(1,149)
Income (loss) before income taxes/net investment loss before taxes																							3,750		2,837
Income tax (provision) benefit																							(862)		(684)
Net income (loss) after taxes/net increase (decrease) on net assets resulting from operations																							2,888		2,153
Balance Sheet Data
Total loans net		66,405					59,973																59,973		66,405		59,973
Total assets		84,924					93,807																93,807		84,924		93,807
Total funds borrowed		68,666					53,719																$ 53,719		$ 68,666		53,719
Selected Financial Ratios
Return on average assets																							4.27%		2.44%
Return on average equity																							9.43%		12.21%
Interest yield																							14.25%		11.39%
Net interest margin																							11.23%		6.90%
Reserve coverage																							0.00%		0.00%	[8]
Delinquency status	[7],[8]																						0.44%		0.15%
Charge-off ratio																							0.00%		1.30%	[9]
Operating Segments [Member] | Medallion Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income																							$ 6,317		$ 3,665
Total interest expense																							10,125		7,962
Net interest income/net investment income																							(3,808)		(4,297)
Provision for loan losses																							41,437		16,331
Net interest income (loss) after loss provision																							(45,245)		(20,628)
Other income (expense), net																							9,742		(10,493)
Income (loss) before income taxes/net investment loss before taxes																							(35,503)		(31,121)
Income tax (provision) benefit																							7,938		7,596
Net income (loss) after taxes/net increase (decrease) on net assets resulting from operations																							(27,565)		(23,525)
Balance Sheet Data
Total loans net		105,022					155,863																155,863		105,022		155,863
Total assets		217,483					273,501																273,501		217,483		273,501
Total funds borrowed		176,825					294,465																$ 294,465		$ 176,825		294,465
Selected Financial Ratios
Return on average assets																							(10.13%)		(9.73%)
Return on average equity																									(48.49%)
Interest yield																							3.58%		2.88%
Net interest margin																							(2.16%)		(3.38%)
Reserve coverage																							15.11%		19.48%
Delinquency status	[7]																						9.43%		2.04%
Charge-off ratio																							7.21%		14.68%
Intersegment Eliminations [Member]
Segment Reporting Disclosure [Line Items]
Total interest income																							$ 1,741		$ 2,308
Total interest expense																							3,792		6,030
Net interest income/net investment income																							(2,051)		(3,722)
Provision for loan losses																									455
Net interest income (loss) after loss provision																							(2,051)		(4,177)
Other income (expense), net																							(6,489)		(7,946)
Income (loss) before income taxes/net investment loss before taxes																							(8,540)		(12,123)
Income tax (provision) benefit																							1,005		3,461
Net income (loss) after taxes/net increase (decrease) on net assets resulting from operations																							(7,535)		(8,662)
Balance Sheet Data
Total loans net		3,362					4,110																4,110		3,362		4,110
Total assets		247,641					204,975																204,975		247,641		204,975
Total funds borrowed		$ 150,898					$ 127,853																$ 127,853		$ 150,898		$ 127,853
Selected Financial Ratios
Return on average assets																							(4.07%)		(3.71%)
Return on average equity																							(12.37%)		(14.26%)

[1] Average borrowings outstanding were $1,138,746, $1,198,124, and $334,022, and the related average borrowing costs were 3.08%, 2.37%, and 4.12% for the years ended December 31, 2019, 2018, and 2017.

[2] Balance includes the nine months ended December 31, 2018 under Bank Holding Company Accounting and the three months ended March 31, 2018 under Investment Company Accounting.

[3] The three months ended March 31, 2018 and earlier quarters have been accounted for under Investment Company Accounting, and subsequent quarters have been accounted for under Bank Holding Company Accounting.

[4] Includes $8,161 of reversal of provision for loan losses related to the deconsolidation of Trust III in the 2018 fourth quarter.

[5] Includes $256 and $870 of net revenues received from Medallion Bank for the years ended December 31, 2018 and 2017, primarily for expense reimbursements. See Notes 6 and 14 for additional information.

[6] Excludes deferred financing costs of $5,105

[7] Loans 90 days or more past due.

[8] Ratio is based on total commercial lending balances, and relates solely to the legacy commercial loan business.

[9] Ratio is based on total commercial lending balances, and relates to the total loan business.