Segment Reporting - Schedule of Segment Data (Detail) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2024		Mar. 31, 2024	Jun. 30, 2023		Mar. 31, 2023	Jun. 30, 2024		Jun. 30, 2023		Dec. 31, 2023
Segment Reporting Disclosure [Line Items]
Total interest income	$ 70,704			$ 61,726			$ 137,774		$ 117,568
Total interest expense	20,836			15,035			39,989		27,275
Net interest income (loss)	49,868			46,691			97,785		90,293
Provision (benefit) for credit losses	18,577			8,476			35,778		12,514
Net interest income (loss) after loss provision	31,291			38,215			62,007		77,779
Other income (loss), net	1,099			1,942			6,502		4,025
Operating expenses	(19,995)			(19,003)			(38,220)		(37,395)
Net income (loss) before taxes	12,395			21,154			30,289		44,409
Income tax (provision) benefit	(3,782)			(5,472)			(10,140)		(11,854)
Net income (loss) after taxes	8,613		$ 11,536	15,682		$ 16,873	20,149		32,555
Income attributable to the non-controlling interest	1,512			1,512			3,024		3,024
Total net income attributable to Medallion Financial Corp.	7,101			14,170			17,125		29,531
Balance Sheet Data
Total loans	2,295,802						2,295,802				$ 2,131,651
Loans	2,385,590			2,156,998			2,385,590		2,156,998		2,215,886
Total assets	2,760,876			2,519,137			2,760,876		2,519,137		$ 2,587,827
Total funds borrowed	$ 2,283,656			$ 2,066,607			$ 2,283,656		$ 2,066,607
Selected Financial Ratios
Return on average assets	1.30%			2.60%			1.55%		2.79%
Return on average stockholders' equity	8.14%			18.24%			9.89%		19.45%
Return on average equity	8.25%			16.52%			9.70%		17.49%
Interest yield	11.52%			11.21%			11.42%		11.01%
Net interest margin, gross	8.12%			8.48%			8.11%		8.45%
Net interest margin, net of allowance	8.42%			8.77%			8.40%		8.75%
Reserve coverage	3.76%			3.48%			3.76%		3.48%
Delinquency status	0.67%	[1]		0.29%	[2]		0.67%	[3]	0.29%	[4]
Charge-off (recovery) ratio	2.20%	[5]		0.74%	[6]		2.68%	[7]	1.51%	[8]
Operating Segments [Member] | Consumer Lending [Member] | Recreation [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 47,490			$ 41,109			$ 91,417		$ 79,008
Total interest expense	10,960			7,580			20,605		13,484
Net interest income (loss)	36,530			33,529			70,812		65,524
Provision (benefit) for credit losses	15,795			10,135			32,825		17,886
Net interest income (loss) after loss provision	20,735			23,394			37,987		47,638
Other income (loss), net	306			0			556		0
Operating expenses	(11,236)			(8,444)			(19,523)		(16,247)
Net income (loss) before taxes	9,805			14,950			19,020		31,391
Income tax (provision) benefit	(3,094)			(3,867)			(6,368)		(8,380)
Net income (loss) after taxes	6,711			11,083			12,652		23,011
Balance Sheet Data
Total loans	1,497,428			1,331,114			1,497,428		1,331,114
Total assets	1,451,947			1,294,925			1,451,947		1,294,925
Total funds borrowed	$ 1,200,977			$ 1,062,309			$ 1,200,977		$ 1,062,309
Selected Financial Ratios
Return on average assets	1.95%			3.59%			1.87%		3.84%
Return on average equity	13.05%			22.94%			12.31%		24.13%
Interest yield	13.30%			13.03%			13.20%		12.93%
Net interest margin, gross	10.23%			10.63%			10.23%		10.72%
Net interest margin, net of allowance	10.69%			11.08%			10.69%		11.18%
Reserve coverage	4.35%			4.07%			4.35%		4.07%
Delinquency status	0.41%	[1]		0.39%	[2]		0.41%	[3]	0.39%	[4]
Charge-off (recovery) ratio	2.99%	[5]		1.86%	[6]		3.64%	[7]	2.57%	[8]
Operating Segments [Member] | Consumer Lending [Member] | Home Improvement [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 17,651			$ 15,292			$ 35,098		$ 28,941
Total interest expense	6,106			4,194			11,740		7,473
Net interest income (loss)	11,545			11,098			23,358		21,468
Provision (benefit) for credit losses	3,279			3,739			4,177		6,820
Net interest income (loss) after loss provision	8,266			7,359			19,181		14,648
Other income (loss), net	3			2			5		3
Operating expenses	(5,457)			(4,388)			(9,571)		(8,382)
Net income (loss) before taxes	2,812			2,973			9,615		6,269
Income tax (provision) benefit	(802)			(769)			(3,219)		(1,674)
Net income (loss) after taxes	2,010			2,204			6,396		4,595
Balance Sheet Data
Total loans	773,184			728,468			773,184		728,468
Total assets	758,840			718,383			758,840		718,383
Total funds borrowed	$ 627,674			$ 589,335			$ 627,674		$ 589,335
Selected Financial Ratios
Return on average assets	1.08%			1.28%			1.72%		1.39%
Return on average equity	7.00%			8.19%			11.04%		8.76%
Interest yield	9.32%			8.79%			9.29%		8.66%
Net interest margin, gross	6.10%			6.38%			6.18%		6.43%
Net interest margin, net of allowance	6.25%			6.53%			6.34%		6.57%
Reserve coverage	2.38%			2.26%			2.38%		2.26%
Delinquency status	0.17%	[1]		0.16%	[2]		0.17%	[3]	0.16%	[4]
Charge-off (recovery) ratio	1.49%	[5]		1.12%	[6]		1.80%	[7]	0.97%	[8]
Operating Segments [Member] | Commercial Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 3,538			$ 2,814			$ 7,183		$ 5,515
Total interest expense	1,056			852			2,154		1,661
Net interest income (loss)	2,482			1,962			5,029		3,854
Provision (benefit) for credit losses	478			(113)			694		214
Net interest income (loss) after loss provision	2,004			2,075			4,335		3,640
Other income (loss), net	(14)			343			4,188		614
Operating expenses	(1,437)			(1,147)			(2,422)		(1,567)
Net income (loss) before taxes	553			1,271			6,101		2,687
Income tax (provision) benefit	(72)			(329)			(2,043)		(718)
Net income (loss) after taxes	481			942			4,058		1,969
Balance Sheet Data
Total loans	110,197			92,637			110,197		92,637
Total assets	105,548			99,713			105,548		99,713
Total funds borrowed	$ 87,304			$ 81,801			$ 87,304		$ 81,801
Selected Financial Ratios
Return on average assets	1.86%			3.76%			7.68%		3.94%
Return on average equity	12.09%			23.97%			49.32%		24.74%
Interest yield	13.08%			11.87%			12.97%		11.71%
Net interest margin, gross	9.18%			8.28%			9.08%		8.18%
Net interest margin, net of allowance	9.57%			8.54%			9.45%		8.43%
Reserve coverage	4.41%			2.72%			4.41%		2.72%
Delinquency status	7.52%	[1]		0.08%	[2]		7.52%	[3]	0.08%	[4]
Charge-off (recovery) ratio	0.00%	[5]		3.80%	[6]		(0.04%)	[7]	1.89%	[8]
Operating Segments [Member] | Taxi Medallion Lending [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 190			$ 787			$ 330		$ 1,097
Total interest expense	25			46			53		113
Net interest income (loss)	165			741			277		984
Provision (benefit) for credit losses	(975)			(5,311)			(1,918)		(12,395)
Net interest income (loss) after loss provision	1,140			6,052			2,195		13,379
Other income (loss), net	334			1,304			973		2,923
Operating expenses	(1,373)			(743)			(2,116)		(2,770)
Net income (loss) before taxes	101			6,613			1,052		13,532
Income tax (provision) benefit	(14)			(1,713)			(352)		(3,612)
Net income (loss) after taxes	87			4,900			700		9,920
Balance Sheet Data
Total loans	3,482			3,448			3,482		3,448
Total assets	7,511			18,724			7,511		18,724
Total funds borrowed	$ 6,213			$ 15,360			$ 6,213		$ 15,360
Selected Financial Ratios
Return on average assets	4.29%			100.63%			14.89%		94.20%
Return on average equity	25.69%			641.63%			90.99%		590.25%
Interest yield	21.62%			83.55%			18.78%		28.80%
Net interest margin, gross	18.78%			78.67%			15.59%		25.84%
Net interest margin, net of allowance	31.77%			166.23%			26.61%		73.52%
Reserve coverage	40.18%			52.76%			40.18%		52.76%
Delinquency status	0.00%	[1]		0.00%	[2]		0.00%	[3]	0.00%	[4]
Charge-off (recovery) ratio	(98.90%)	[5]		(525.21%)	[6]		(100.16%)	[7]	(124.01%)	[8]
Intersegment Eliminations [Member]
Segment Reporting Disclosure [Line Items]
Total interest income	$ 1,835			$ 1,724			$ 3,746		$ 3,007
Total interest expense	2,689			2,363			5,437		4,544
Net interest income (loss)	(854)			(639)			(1,691)		(1,537)
Provision (benefit) for credit losses	0			26			0		(11)
Net interest income (loss) after loss provision	(854)			(665)			(1,691)		(1,526)
Other income (loss), net	470			293			780		485
Operating expenses	(492)			(4,281)			(4,588)		(8,429)
Net income (loss) before taxes	(876)			(4,653)			(5,499)		(9,470)
Income tax (provision) benefit	200			1,206			1,842		2,530
Net income (loss) after taxes	(676)			(3,447)			(3,657)		(6,940)
Balance Sheet Data
Total loans	1,299			1,331			1,299		1,331
Total assets	437,030			387,392			437,030		387,392
Total funds borrowed	$ 361,488			$ 317,802			$ 361,488		$ 317,802
Selected Financial Ratios
Return on average assets	(0.61%)			(3.69%)			(1.69%)		(3.70%)
Return on average equity	(3.88%)			(22.83%)			(10.64%)		(23.24%)

[1] Loans 90 days or more past due.

[2] Loans 90 days or more past due.

[3] Loans 90 days or more past due.

[4] Loans 90 days or more past due.

[5] Negative balances indicate net recoveries for the period.

[6] Negative balances indicate net recoveries for the period.

[7] Negative balances indicate net recoveries for the period.

[8] Negative balances indicate net recoveries for the period.