Medallion Bank - Schedule of Balance Sheet and Net Investment (Detail) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Loans			$ 864,819
Investment securities, at fair value			43,478
Net investments			908,297
Cash			110,233
Other assets, net			58,827
Total assets		$ 1,571,407	1,077,357
Other liabilities			3,836
Due to affiliates			1,055
Deposits and other borrowings, including accrued interest payable			908,236
Total liabilities			913,127
Medallion Bank equity	[1]		164,230
Total liabilities and equity			1,077,357
Investment in other controlled subsidiaries			11,449
Medallion Bank and Other Controlled Subsidiaries [Member]
Debt Securities, Available-for-sale [Line Items]
Total investment in Medallion Bank and other controlled subsidiaries			$ 302,147

[1] Includes $152,267 of unrealized appreciation on Medallion Bank, in excess of Medallion Bank's book value as of December 31, 2017.