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Share-Based Compensation Plans - Employee Shares (Details) - Tradeweb Markets LLC - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Predecessor |  |  |  |
Activity of the Employee Shares |  |  |  |
Employee Shares compensation payable |  |  | $ 0 |
Compensation expense relating to PRSUs, options and shares |  | $ 15,949,000 | $ 26,100,000 | $ 19,032,000
Predecessor | Class C common stock |  |  |  |
Activity of the Employee Shares |  |  |  |
Outstanding, beginning of period | 447 | 447 | 504 | 528
Purchased |  | 0 | 5 |
Sold |  |  | (62) | (24)
Outstanding, end of period |  | 447 | 447 | 504
Predecessor | Class P(C) Shares |  |  |  |
Activity of the Employee Shares |  |  |  |
Outstanding, beginning of period | 2 | 2 | 2 | 2
Purchased |  | 0 | 0 |
Sold |  |  | 0 | 0
Outstanding, end of period |  | 2 | 2 | 2
Predecessor | Class P-1(C) Shares |  |  |  |
Activity of the Employee Shares |  |  |  |
Outstanding, beginning of period | 232 | 0 | 0 | 0
Purchased |  | 232 | 0 |
Sold |  |  | 0 | 0
Outstanding, end of period |  | 232 | 0 | 0
Successor |  |  |  |
Activity of the Employee Shares |  |  |  |
Period of time to determine classification as compensation payable | 6 months |  |  |
Employee Shares compensation payable | $ 6,727,000 |  |  |
Compensation expense relating to PRSUs, options and shares | $ 9,413,000 |  |  |
Successor | Class C common stock |  |  |  |
Activity of the Employee Shares |  |  |  |
Outstanding, beginning of period | 447 |  |  |
Sold | 0 |  |  |
Outstanding, end of period | 447 | 447 |  |
Successor | Class P(C) Shares |  |  |  |
Activity of the Employee Shares |  |  |  |
Outstanding, beginning of period | 2 |  |  |
Sold | 0 |  |  |
Outstanding, end of period | 2 | 2 |  |
Successor | Class P-1(C) Shares |  |  |  |
Activity of the Employee Shares |  |  |  |
Outstanding, beginning of period | 232 |  |  |
Sold | 0 |  |  |
Outstanding, end of period | 232 | 232 |  |

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- Definition The number of securities classified as temporary equity that have been issued and are held by the entity's shareholders. Securities outstanding equals securities issued minus securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(27)(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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