Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill	$ 308.5	$ 308.5	$ 308.5
Accumulated impairment	(33.9)	(33.9)	(33.9)
Beginning balance	274.6	274.6
Additions	0.0	0.0
Impairments	0.0	0.0
Disposals	0.0	0.0
Ending balance	274.6	274.6
Quant & Solutions
Goodwill [Line Items]
Goodwill	22.1	22.1	22.1
Accumulated impairment	(1.8)	(1.8)	(1.8)
Beginning balance	20.3	20.3
Additions	0.0	0.0
Impairments	0.0	0.0
Disposals	0.0	0.0
Ending balance	20.3	20.3
Alternatives
Goodwill [Line Items]
Goodwill	153.1	153.1	153.1
Accumulated impairment	(5.0)	(5.0)	(5.0)
Beginning balance	148.1	148.1
Additions	0.0	0.0
Impairments	0.0	0.0
Disposals	0.0	0.0
Ending balance	148.1	148.1
Liquid Alpha
Goodwill [Line Items]
Goodwill	133.3	133.3	133.3
Accumulated impairment	(27.1)	(27.1)	$ (27.1)
Beginning balance	106.2	106.2
Additions	0.0	0.0
Impairments	0.0	0.0
Disposals	0.0	0.0
Ending balance	$ 106.2	$ 106.2