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Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance	$ 525,500,000
Goodwill, impairment loss	(30,200,000)		$ 0
Amortization of other intangible assets	(9,200,000)	$ (5,100,000)
Goodwill, ending balance	613,400,000		525,500,000
Fresh Insurance Services Group Limited
Acquired Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of other assets	1,500,000
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance	525,500,000	394,700,000	394,700,000
Acquisitions of businesses	116,800,000	0
Goodwill, foreign currency translation gain (loss)	1,500,000	(2,500,000)
Goodwill, impairment loss	(30,200,000)	0
Measurement period adjustments	(200,000)	200,000
Goodwill, ending balance	613,400,000	392,400,000	525,500,000
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets (excluding goodwill), beginning balance	256,900,000	260,000,000.0	260,000,000.0
Acquisitions of businesses	175,700,000	0
Other intangible assets, foreign currency translation gain (loss)	200,000	(500,000)
Measurement period adjustments	0	0
Amortization of other intangible assets	(9,200,000)	(5,100,000)
Other intangible assets (excluding goodwill), ending balance	423,600,000	254,400,000	256,900,000
Total Goodwill and Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets, gross (including goodwill), beginning balance	782,400,000	654,700,000	654,700,000
Acquisitions of businesses	292,500,000	0
Other intangible assets, foreign currency translation gain (loss)	1,700,000	(3,000,000.0)
Goodwill, impairment loss	(30,200,000)	0
Measurement period adjustments	(200,000)	200,000
Amortization of other intangible assets	(9,200,000)	(5,100,000)
Other intangible assets, gross (including goodwill), ending balance	$ 1,037,000,000.0	$ 646,800,000	$ 782,400,000

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