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Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended
	May 06, 2020	May 05, 2020	Apr. 27, 2020	Apr. 08, 2019	Mar. 31, 2020	Mar. 31, 2019	May 01, 2020
Subsequent Event [Line Items]
Cash dividend declared Per Share					$ 0.08
Capital distributions						$ 20,000
Received net proceeds					$ 35,422
Class A common stock
Subsequent Event [Line Items]
Shares issued					2,341,171
Class A common stock \| Underwriter
Subsequent Event [Line Items]
Shares issued				6,000,000
Class B common stock
Subsequent Event [Line Items]
Shares issued				96,933,192
Subsequent Event
Subsequent Event [Line Items]
Capital distributions		$ 18,100
Subsequent Event \| Trade Web Markets LLC
Subsequent Event [Line Items]
Ownership interest							80.00%
Ownership percentage, Continuing LLC Owners							20.00%
Subsequent Event \| Trade Web Markets LLC
Subsequent Event [Line Items]
Received net proceeds			$ 626,300
Shares repurchased			12,238,827
Subsequent Event \| Follow On Offering
Subsequent Event [Line Items]
Share Price (per share)			$ 50.25
Subsequent Event \| Underwriter
Subsequent Event [Line Items]
Shares issued			1,674,162
Share Price (per share)			$ 50.25
Subsequent Event \| Class A common stock
Subsequent Event [Line Items]
Cash dividend declared Per Share	$ 0.08
Shares issued			12,835,245
Subsequent Event \| Class A common stock \| Trade Web Markets LLC
Subsequent Event [Line Items]
Shares repurchased			596,418
Subsequent Event \| Class B common stock
Subsequent Event [Line Items]
Cash dividend declared Per Share	$ 0.08