Segment Reporting - Schedule of Segment Data (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025		Mar. 31, 2024		Dec. 31, 2024
Segment Reporting Disclosure [Line Items]
Total interest income	$ 75,425		$ 67,070
Total interest expense	24,013		19,153
Net interest income	51,412		47,917
Provision (benefit) for credit losses	22,014		17,201
Net interest income after provision for credit losses	29,398		30,716
Other income, net	11,599		5,403
Operating expenses	(20,758)		(18,225)
Income before income taxes	20,239		17,894
Income tax (provision) benefit	(6,713)		(6,358)
Net income (loss) after taxes	13,526		11,536
Income attributable to the non-controlling interest	1,512		1,512
Net income attributable to Medallion Financial Corp.	12,014		10,024
Balance Sheet Data
Total loans, gross	2,261,334				$ 2,265,428
Net loans	2,486,433	[1]	2,228,426		2,491,022
Total assets	2,847,738		2,618,762		$ 2,868,606
Total funds borrowed	$ 2,342,373		$ 2,145,596
Selected Financial Ratios
Return on average assets	1.93%		1.80%
Return on average stockholders' equity	12.96%		11.65%
Return on average equity	12.32%		11.18%
Interest yield	11.65%		11.34%
Net interest margin, gross	7.94%		8.10%
Net interest margin, net of allowance	8.25%		8.39%
Reserve coverage	4.25%	[2]	3.76%	[3]
Delinquency status	1.20%	[4]	0.74%	[5]
Charge-off (recovery) ratio	3.10%	[6]	3.20%	[7]
Operating Segments [Member] | Recreation [Member]
Selected Financial Ratios
Charge-off (recovery) ratio	4.32%
Operating Segments [Member] | Consumer Lending [Member] | Recreation [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 50,466		$ 43,927
Total interest expense	12,041		9,645
Net interest income	38,425		34,282
Provision (benefit) for credit losses	16,870		17,030
Net interest income after provision for credit losses	21,555		17,252
Other income, net	400		250
Operating expenses	(9,964)		(8,287)
Income before income taxes	11,991		9,215
Income tax (provision) benefit	(3,977)		(3,274)
Net income (loss) after taxes	8,014		5,941
Balance Sheet Data
Total loans, gross	1,545,844	[1]	1,365,165
Total assets	1,495,150		1,322,761
Total funds borrowed	$ 1,229,818		$ 1,083,760
Selected Financial Ratios
Return on average assets	2.17%		1.82%
Return on average equity	13.37%		11.44%
Interest yield	13.27%		13.17%
Net interest margin, gross	10.10%		10.28%
Net interest margin, net of allowance	10.59%		10.75%
Reserve coverage	5.00%	[2]	4.40%	[3]
Delinquency status	0.48%	[4]	0.48%	[5]
Charge-off (recovery) ratio	4.67%	[6]	4.36%	[7]
Operating Segments [Member] | Consumer Lending [Member] | Home Improvement [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 19,771		$ 17,447
Total interest expense	6,964		5,634
Net interest income	12,807		11,813
Provision (benefit) for credit losses	2,845		898
Net interest income after provision for credit losses	9,962		10,915
Other income, net	2		2
Operating expenses	(4,984)		(4,114)
Income before income taxes	4,980		6,803
Income tax (provision) benefit	(1,652)		(2,417)
Net income (loss) after taxes	3,328		4,386
Balance Sheet Data
Total loans, gross	812,381	[1]	752,262
Total assets	795,868		738,551
Total funds borrowed	$ 654,632		$ 605,107
Selected Financial Ratios
Return on average assets	1.68%		2.38%
Return on average equity	10.33%		14.93%
Interest yield	9.78%		9.28%
Net interest margin, gross	6.33%		6.28%
Net interest margin, net of allowance	6.50%		6.45%
Reserve coverage	2.49%	[2]	2.38%	[3]
Delinquency status	0.19%	[4]	0.18%	[5]
Charge-off (recovery) ratio	1.55%	[6]	2.12%	[7]
Operating Segments [Member] | Commercial Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 3,343		$ 3,645
Total interest expense	1,053		1,098
Net interest income	2,290		2,547
Provision (benefit) for credit losses	3,114		216
Net interest income after provision for credit losses	(824)		2,331
Other income, net	9,642		4,202
Operating expenses	(1,473)		(985)
Income before income taxes	7,345		5,548
Income tax (provision) benefit	(2,436)		(1,971)
Net income (loss) after taxes	4,909		3,577
Balance Sheet Data
Total loans, gross	116,059	[1]	106,570
Total assets	109,565		102,331
Total funds borrowed	$ 90,121		$ 83,842
Selected Financial Ratios
Return on average assets	18.45%		13.50%
Return on average equity	113.46%		84.71%
Interest yield	12.05%		12.99%
Net interest margin, gross	8.25%		9.08%
Net interest margin, net of allowance	8.71%		9.43%
Reserve coverage	7.04%	[2]	4.11%	[3]
Delinquency status	17.63%	[4]	7.80%	[5]
Charge-off (recovery) ratio	0.47%	[6]	(0.07%)	[7]
Operating Segments [Member] | Taxi Medallion Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 80		$ 140
Total interest expense	12		28
Net interest income	68		112
Provision (benefit) for credit losses	(815)		(944)
Net interest income after provision for credit losses	883		1,056
Other income, net	844		639
Operating expenses	(983)		(743)
Income before income taxes	744		952
Income tax (provision) benefit	(247)		(338)
Net income (loss) after taxes	497		614
Balance Sheet Data
Total loans, gross	1,650	[1]	3,560
Total assets	6,855		8,611
Total funds borrowed	$ 5,638		$ 7,055
Selected Financial Ratios
Return on average assets	30.14%		23.68%
Return on average equity	185.45%		148.65%
Interest yield	19.12%		15.59%
Net interest margin, gross	16.25%		12.47%
Net interest margin, net of allowance	21.87%		21.57%
Reserve coverage	23.32%	[2]	42.19%	[3]
Delinquency status	0.00%	[4]	0.00%	[5]
Charge-off (recovery) ratio	(157.97%)	[6]	(101.47%)	[7]
Intersegment Eliminations [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 1,765		$ 1,911
Total interest expense	3,943		2,748
Net interest income	(2,178)		(837)
Provision (benefit) for credit losses	0		1
Net interest income after provision for credit losses	(2,178)		(838)
Other income, net	711		310
Operating expenses	(3,354)		(4,096)
Income before income taxes	(4,821)		(4,624)
Income tax (provision) benefit	1,599		1,642
Net income (loss) after taxes	(3,222)		(2,982)
Balance Sheet Data
Total loans, gross	10,499	[1]	869
Total assets	440,300		446,508
Total funds borrowed	$ 362,164		$ 365,832
Selected Financial Ratios
Return on average assets	(2.94%)		(2.78%)
Return on average equity	(18.04%)		(17.47%)

[1] Inclusive of recreation and strategic partnership loans held for sale, at lower of amortized cost or fair value.

[2] Allowance for credit loss as a percent of gross loans held for investment and excludes loans held for sale.

[3] Allowance for credit loss as a percent of gross loans held for investment and excludes loans held for sale.

[4] Loans 90 days or more past due as a percent of total loans.

[5] Loans 90 days or more past due as a percent of total loans.

[6] Charge-off ratio in the recreation lending segment was 4.32% when including loans held for sale.

[7] Net charge-offs as a percent of annual average total gross loans.