Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance			$ 142.3
Amortization of other intangible assets	$ (1.4)	$ (2.0)	(3.4)	$ (3.1)
Goodwill, ending balance	175.5		175.5
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance	201.8	151.5	142.3	19.2
Acquisition of businesses			59.5	15.8
Attribution of acquisition date fair value estimates between goodwill and other intangible assets	(22.9)	(9.3)	(22.9)	(9.3)
Measurement period adjustments	(3.4)	(0.4)	(3.4)	(0.7)
Amortization of other intangible assets	0.0	0.0	0.0	0.0
Goodwill, ending balance	175.5	141.8	175.5	141.8
Goodwill | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill acquired			0.0	116.8
Other
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets (excluding goodwill), beginning balance	196.2	201.1	198.2	26.4
Acquisition of businesses			0.0	0.0
Attribution of acquisition date fair value estimates between goodwill and other intangible assets	22.9	9.3	22.9	9.3
Measurement period adjustments	0.0	0.0		0.1
Amortization of other intangible assets	(1.4)	(2.0)	(3.4)	(3.1)
Other intangible assets (excluding goodwill), ending balance	217.7	208.4	217.7	208.4
Other | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired			0.0	175.7
Total Goodwill and Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets, gross (including goodwill), beginning balance	398.0	352.6	340.5	45.6
Acquisition of businesses			59.5	15.8
Attribution of acquisition date fair value estimates between goodwill and other intangible assets	0.0	0.0	0.0	0.0
Measurement period adjustments	(3.4)	(0.4)	(3.4)	(0.6)
Amortization of other intangible assets	(1.4)	(2.0)	(3.4)	(3.1)
Other intangible assets, gross (including goodwill), ending balance	$ 393.2	$ 350.2	393.2	350.2
Total Goodwill and Other Intangible Assets | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill and other intangible assets acquired			$ 0.0	$ 292.5