Segment Reporting - Schedule of Segment Data (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Disclosure [Line Items]
Total interest income	$ 33,152		$ 65,796	$ 3,287	[1]
Total interest expense	8,887		16,812	20,363	[1],[2]
Net interest income	24,265		48,984	49,466	[1]
Provision for loan losses	18,205		48,781	48,781	[1]
Net interest income after loss provision	6,060		203	685	[1]
Sponsorship and race winnings	5,371		10,599	10,599	[1]
Race team related expenses	(2,876)		(5,416)	5,416	[1]
Other income (expense)	(12,518)		(27,254)
Loss before income taxes/net investment loss before taxes	(3,963)		(21,868)	(25,434)	[1],[3]
Income tax benefit (provision)	117	$ 6,155	4,138	4,778		$ 15,144
Net Income (loss) after tax	(3,846)		(17,730)	(32,604)	[1]
Balance Sheet Data
Total loans, net	1,060,061		1,060,061	1,060,061
Total assets	1,571,407		1,571,407	1,571,407			$ 1,077,357
Total funds borrowed	$ 1,265,074		$ 1,265,074	1,265,074
Selected Financial Ratios
Return on assets	(1.19%)		(2.51%)
Return on equity	(6.59%)		(13.34%)
Interest yield	10.75%		10.91%
Net interest margin	7.94%		8.17%
Reserve coverage	2.71%		2.71%
Delinquency ratio	1.29%		1.29%
Charge off ratio	3.69%		3.53%
RPAC Racing, LLC [Member]
Segment Reporting Disclosure [Line Items]
Total interest expense	$ 40		$ 81
Net interest income	(40)		(81)
Net interest income after loss provision	(40)		(81)
Sponsorship and race winnings	5,371		10,599
Race team related expenses	(2,876)		(5,416)
Other income (expense)	(1,887)		(4,124)
Loss before income taxes/net investment loss before taxes	568		978
Income tax benefit (provision)	(107)		(150)
Net Income (loss) after tax	461		828
Balance Sheet Data
Total assets	36,237		36,237	36,237
Total funds borrowed	$ 7,614		$ 7,614	7,614
Selected Financial Ratios
Return on assets	4.94%		4.46%
Return on equity	42.83%		38.67%
Operating Segments [Member] | Consumer Lending [Member] | Recreation [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 24,001		$ 46,133
Total interest expense	2,306		4,442
Net interest income	21,695		41,691
Provision for loan losses	4,423		9,133
Net interest income after loss provision	17,272		32,558
Other income (expense)	(3,160)		(8,680)
Loss before income taxes/net investment loss before taxes	14,112		23,878
Income tax benefit (provision)	(3,979)		(6,141)
Net Income (loss) after tax	10,133		17,737
Balance Sheet Data
Total loans, net	572,995		572,995	572,995
Total assets	582,610		582,610	582,610
Total funds borrowed	$ 431,868		$ 431,868	431,868
Selected Financial Ratios
Return on assets	6.80%		6.14%
Return on equity	27.77%		25.48%
Interest yield	15.87%		15.88%
Net interest margin	14.34%		14.35%
Reserve coverage	0.50%		0.50%
Delinquency ratio	0.55%		0.55%
Charge off ratio	3.19%		3.26%
Operating Segments [Member] | Consumer Lending [Member] | Home Improvement [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 3,968		$ 8,605
Total interest expense	709		1,448
Net interest income	3,259		7,157
Provision for loan losses	598		1,475
Net interest income after loss provision	2,661		5,682
Other income (expense)	400		(1,285)
Loss before income taxes/net investment loss before taxes	3,061		4,397
Income tax benefit (provision)	(863)		(1,159)
Net Income (loss) after tax	2,198		3,238
Balance Sheet Data
Total loans, net	168,781		168,781	168,781
Total assets	175,333		175,333	175,333
Total funds borrowed	$ 132,914		$ 132,914	132,914
Selected Financial Ratios
Return on assets	4.57%		3.42%
Return on equity	19.99%		15.22%
Interest yield	8.10%		8.94%
Net interest margin	6.65%		7.44%
Reserve coverage	0.51%		0.51%
Delinquency ratio	0.10%		0.10%
Charge off ratio	1.34%		1.27%
Operating Segments [Member] | Commercial Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 2,637		$ 4,959
Total interest expense	681		1,336
Net interest income	1,956		3,623
Provision for loan losses	(75)		100
Net interest income after loss provision	2,031		3,523
Other income (expense)	(934)		(2,044)
Loss before income taxes/net investment loss before taxes	1,097		1,479
Income tax benefit (provision)	(254)		(339)
Net Income (loss) after tax	843		1,140
Balance Sheet Data
Total loans, net	82,458		82,458	82,458
Total assets	90,380		90,380	90,380
Total funds borrowed	$ 71,655		$ 71,655	71,655
Selected Financial Ratios
Return on assets	3.35%		2.15%
Return on equity	6.99%		4.81%
Interest yield	12.87%		12.24%
Net interest margin	9.54%		8.94%
Reserve coverage	0.12%		0.12%
Delinquency ratio	0.51%		0.51%
Charge off ratio	0.00%		0.00%
Operating Segments [Member] | Medallion Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 2,126		$ 5,315
Total interest expense	3,672		7,045
Net interest income	(1,546)		(1,730)
Provision for loan losses	13,259		38,073
Net interest income after loss provision	(14,805)		(39,803)
Other income (expense)	(4,077)		(6,888)
Loss before income taxes/net investment loss before taxes	(18,882)		(46,691)
Income tax benefit (provision)	4,371		10,528
Net Income (loss) after tax	(14,511)		(36,163)
Balance Sheet Data
Total loans, net	235,827		235,827	235,827
Total assets	369,763		369,763	369,763
Total funds borrowed	$ 399,750		$ 399,750	399,750
Selected Financial Ratios
Return on assets	(15.23%)		(18.49%)
Interest yield	3.41%		4.03%
Net interest margin	(2.48%)		(1.31%)
Reserve coverage	9.81%		9.81%
Delinquency ratio	4.06%		4.06%
Charge off ratio	10.35%		9.66%
Intersegment Eliminations [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 420		$ 784
Total interest expense	1,479		2,460
Net interest income	(1,059)		(1,676)
Net interest income after loss provision	(1,059)		(1,676)
Other income (expense)	(2,860)		(4,233)
Loss before income taxes/net investment loss before taxes	(3,919)		(5,909)
Income tax benefit (provision)	949		1,399
Net Income (loss) after tax	(2,970)		(4,510)
Balance Sheet Data
Total assets	317,084		317,084	317,084
Total funds borrowed	$ 221,273		$ 221,273	$ 221,273
Selected Financial Ratios
Return on assets	(4.60%)		(3.67%)
Return on equity	(16.79%)		(11.85%)

[1] Balance includes the six months ended September 30, 2018 under Bank Holding Company Accounting and three months ended March 31, 2018 under Investment Company Accounting.

[2] Average borrowings outstanding were $1,255,945 and $1,226,896, and the related average borrowing costs were 2.81% and 2.22% for the three and nine months ended September 30, 2018, and were $330,885 and $335,907 and 4.25% and 4.09% for the comparable 2017 periods.

[3] Includes $256 of net revenues received from Medallion Bank for the nine months ended September 30, 2018 and $184 and $641 for the three and nine months ended September 30, 2017, primarily for expense reimbursements. See Notes 6 and 13 for additional information.