Consolidated Statement of Changes in Stockholders' Equity and Changes in Net Assets - USD ($) $ in Thousands		Total	Common Stock [Member]	Preferred Stock [Member]	Capital in Excess of Par [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Parent [Member]	Noncontrolling Interest [Member]	Accumulated Undistributed Net Investment Loss [Member]	Net Unrealized Appreciation on Investment Net of Tax [Member]
Balance at Dec. 31, 2016		$ 286,096
Ending balance at Dec. 31, 2017		287,159	$ 273		$ 273,716	$ (24,919)			$ 287,159
Ending balance (Investment Company Accounting [Member]) at Dec. 31, 2017											$ (65,592)	$ 103,681
Ending balance, shares at Dec. 31, 2017			27,294,327			(2,951,243)
Net income (loss)	[1]	(14,874)
Net increase (decrease) in net assets resulting from operations		(14,874)							(14,874)
Net increase (decrease) in net assets resulting from operations | Investment Company Accounting [Member]											(38,299)	23,425
Stock-based compensation		152	$ 1		151				152
Issuance of restricted stock, net, shares			95,726
Ending balance at Mar. 31, 2018		272,437	$ 274		273,867	$ (24,919)			272,437
Ending balance (Investment Company Accounting [Member]) at Mar. 31, 2018											(103,891)	127,106
Ending balance, shares at Mar. 31, 2018			27,390,053			(2,951,243)
Adoption of Bank Holding Company Accounting at Mar. 31, 2018							$ 23,215
Adoption of Bank Holding Company Accounting (Investment Company Accounting [Member]) at Mar. 31, 2018											103,891	(127,106)
Balance at April 2, 2018 at Mar. 31, 2018		299,502	$ 274		273,867	$ (24,919)	23,215		272,437	$ 27,065
Balance at Dec. 31, 2017		287,159	$ 273		273,716	$ (24,919)			287,159
Balance (Investment Company Accounting [Member]) at Dec. 31, 2017											(65,592)	103,681
Balance, shares at Dec. 31, 2017			27,294,327			(2,951,243)
Net income (loss)	[2]	(22,739)
Ending balance at Dec. 31, 2018		$ 290,204	$ 274		274,292	$ (24,919)	13,043	$ (82)	262,608	27,596
Ending balance, shares at Dec. 31, 2018		24,434,357	27,385,600			(2,951,243)
Balance at Mar. 31, 2018		$ 272,437	$ 274		273,867	$ (24,919)			272,437
Balance (Investment Company Accounting [Member]) at Mar. 31, 2018											$ (103,891)	$ 127,106
Balance, shares at Mar. 31, 2018			27,390,053			(2,951,243)
Net income (loss)		(7,865)					(10,172)		(10,172)	2,307
Distributions to non-controlling interest		(1,776)								(1,776)
Stock-based compensation		425			425				425
Forfeiture of restricted stock, net, shares			(4,453)
Net change in unrealized gains (losses) on investments, net of tax		(82)						(82)	(82)
Ending balance at Dec. 31, 2018		$ 290,204	$ 274		274,292	$ (24,919)	13,043	(82)	262,608	27,596
Ending balance, shares at Dec. 31, 2018		24,434,357	27,385,600			(2,951,243)
Net income (loss)		$ 1,996					(1,762)		(1,762)	3,758
Non-controlling interest equity raised by Medallion Bank	[3]	42,485								42,485
Distributions to non-controlling interest		(2,519)								(2,519)
Stock-based compensation		1,221	$ 2		1,219				1,221
Issuance of restricted stock, net		0	$ 0	$ 0	0	$ 0	0	0	0	0
Issuance of restricted stock, net, shares			216,148
Forfeiture of restricted stock, net		0	$ 0	$ 0	0	0	0	0	0	0
Forfeiture of restricted stock, net, shares			(3,946)
Net change in unrealized gains (losses) on investments, net of tax		1,081						1,081	1,081
Ending balance at Dec. 31, 2019		$ 334,468	$ 276		$ 275,511	$ (24,919)	$ 11,281	$ 999	$ 263,148	$ 71,320
Ending balance, shares at Dec. 31, 2019		24,646,559	27,597,802			(2,951,243)

[1] 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.

[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] Refer to Note 21 for details.