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Employee Savings Plan - 401(k) Plan (Details) - Tradeweb Markets LLC - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Successor | U.S.
Employees Savings Plan
401(k) Savings Plan	us-gaap:QualifiedPlanMember		us-gaap:QualifiedPlanMember
Employees' voluntary contribution percentage			75.00%
Company match, as a percent of the employee's contribution			100.00%
Employer match limit, as a percent of employee's compensation			4.00%
Expense recognized	$ 738,000
Successor | UK and Asia
Employees Savings Plan
Expense recognized	$ 423,000
Predecessor | U.S.
Employees Savings Plan
Expense recognized		$ 3,758,000		$ 4,137,000	$ 4,179,000
Predecessor | UK and Asia
Employees Savings Plan
Expense recognized		$ 1,113,000		$ 1,242,000	$ 1,181,000

X

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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- Definition

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+ References

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

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- Definition

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+ References

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

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- Definition

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+ References

No definition available.

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