Stockholder's Equity - Amendments and Restatement of Certificate of Incorporation (Details)	9 Months Ended
	Sep. 30, 2020 Vote $ / shares shares	Dec. 31, 2019 $ / shares shares	Apr. 08, 2019	Apr. 03, 2019 $ / shares shares
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares	250,000,000	250,000,000		250,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.00001	$ 0.00001		$ 0.00001
Tradeweb Markets LLC
Class of Stock [Line Items]
Threshold percentage of economic interest for conversion	10.00%
Class A Common Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares) | shares	1,000,000,000			1,000,000,000
Common Stock, par value (in dollars per share) | $ / shares	$ 0.00001			$ 0.00001
Votes | Vote	1
Cancellation ratio	1
Class A Common Stock | Tradeweb Markets LLC
Class of Stock [Line Items]
Conversion ratio	1
Class B Common Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares) | shares	450,000,000			450,000,000
Common Stock, par value (in dollars per share) | $ / shares	$ 0.00001			$ 0.00001
Votes | Vote	10
Cancellation ratio	1
Class C Common Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares) | shares	350,000,000			350,000,000
Common Stock, par value (in dollars per share) | $ / shares	$ 0.00001			$ 0.00001
Votes | Vote	1
Cancellation ratio	1
Class C Common Stock | Tradeweb Markets LLC
Class of Stock [Line Items]
Conversion ratio	1
Class D Common Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares) | shares	300,000,000			300,000,000
Common Stock, par value (in dollars per share) | $ / shares	$ 0.00001			$ 0.00001
Votes | Vote	10
Cancellation ratio	1
Voting power threshold percentage to require conversion of shares			4.90%
Class D Common Stock | Minimum
Class of Stock [Line Items]
Voting power threshold percentage to require conversion of shares			4.90%