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Related Party Transactions - Convertible Term Note (Details) - Tradeweb Markets LLC - Predecessor - TR - Convertible term note - USD ($) |  | 12 Months Ended
--- | --- | ---
May 05, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2013
Related Party Transactions |  |  |  |
Amount of loan |  |  |  | $ 29,285,000
Debt interest expense |  | $ 455,000 | $ 1,339,000 |
LIBOR |  |  |  |
Related Party Transactions |  |  |  |
Variable interest rate basis |  |  |  | LIBOR
Basis spread on variable rate |  |  |  | 1.50%
Variable rate additional adjustment |  |  |  | 3.00%
Effective interest rate percentage |  | 4.50% | 4.50% |
Class A common stock |  |  |  |
Related Party Transactions |  |  |  |
Number of equity shares issued upon conversion of debt | 1,835 |  |  |
Share Price (per share) | $ 15,958 |  |  |

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