Significant Accounting Policies - Furniture, Equipment, Purchased Software, Leasehold Improvements and Software Development Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Software development costs
Furniture, Equipment, Purchased Software and Leasehold Improvements
Useful life	3 years
Amortization of pushdown accounting allocation	9 years
Software development costs | NFI Acquisition
Furniture, Equipment, Purchased Software and Leasehold Improvements
Useful life of intangible assets	1 year
Software development costs | Yieldbroker Acquisition
Furniture, Equipment, Purchased Software and Leasehold Improvements
Useful life of intangible assets	1 year
Minimum
Furniture, Equipment, Purchased Software and Leasehold Improvements
Useful life of intangible assets	4 years
Maximum
Furniture, Equipment, Purchased Software and Leasehold Improvements
Useful life of intangible assets	13 years
Furniture, Equipment, Purchased Software and Leasehold Improvements
Furniture, Equipment, Purchased Software and Leasehold Improvements
Accumulated depreciation and amortization	$ 95.8	$ 73.8
Depreciation expense	$ 21.3	$ 19.5	$ 20.9
Furniture, Equipment, Purchased Software and Leasehold Improvements | Minimum
Furniture, Equipment, Purchased Software and Leasehold Improvements
Useful life	3 years
Furniture, Equipment, Purchased Software and Leasehold Improvements | Maximum
Furniture, Equipment, Purchased Software and Leasehold Improvements
Useful life	7 years