Commission Management Payable (Notes)	12 Months Ended
	Dec. 31, 2019
Commission Management Payable [Abstract]
Commission management payable [Text Block]	Commission Management PayableThe Company receives a gross commission from various clearing brokers, which is then used to fund commission sharing and recapture arrangements, less the portion retained as income to the Company. Accrued commission sharing and commission recapture payable of $71.6 million and $95.3 million, as of December 31, 2019 and 2018, respectively, are classified as commission management payable in the accompanying consolidated statements of financial condition.