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Schedule of Pre-Tax Changes in Unrealized and Realized Gains and Losses in Investment Portfolio (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2018
Net change in unrealized appreciation (depreciation) on investments |  |  |
Unrealized appreciation |  | $ 37,797 |
Unrealized depreciation |  | 40,067 |
Net unrealized appreciation on investments in Medallion Bank and other controlled subsidiaries | [1] |  | $ 29,115
Net realized gains (losses) on investments |  |  |
Total | [1],[2] |  | $ (34,745)
Investment Company Accounting [Member] |  |  |
Net change in unrealized appreciation (depreciation) on investments |  |  |
Unrealized appreciation |  | (998) |
Unrealized depreciation |  | (38,152) |
Realized losses |  | 34,747 |
Net unrealized losses on investments other than securities and other assets |  | (1,915) |
Total |  | 22,797 |
Net realized gains (losses) on investments |  |  |
Realized losses |  | (34,747) |
Direct charge-offs |  | 2 |
Total |  | (34,745) |
Medallion Financing Trust I [Member] | Investment Company Accounting [Member] |  |  |
Net change in unrealized appreciation (depreciation) on investments |  |  |
Net unrealized appreciation on investments in Medallion Bank and other controlled subsidiaries |  | $ 29,115 |
[1] | 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.
[2] | There were no net losses on investment securities of affiliated issuers for the year ended December 31, 2018.

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