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Goodwill and Other Intangible Assets - Goodwill and Intangible Assets Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning balance	$ 394.7
Ending balance	525.5	$ 394.7
Finite-lived Intangible Assets [Roll Forward]
Amortization	(28.3)	(21.8)	$ (18.8)
Goodwill and Intangible Assets [Roll Forward]
Goodwill, impairment loss	0.0	7.6
Total other intangible assets
Goodwill [Roll Forward]
Contingent considerations	23.2	26.8
Measurement period adjustments	6.6	5.9
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	260.0	157.6
Acquisitions of businesses	0.0	34.6
Impairments	(6.2)	(2.8)
Foreign currency translation	1.6	0.7
Amortization	(28.3)	(21.8)
Ending balance	256.9	260.0	157.6
Renewal rights
Finite-lived Intangible Assets [Roll Forward]
Acquisitions of businesses	0.0	82.5
Goodwill
Goodwill [Roll Forward]
Beginning balance	394.7	379.9
Acquisitions of businesses	140.0	64.8
Acquisition of collector car renewal rights	0.0	0.0
Dispositions of businesses	0.0
Contingent considerations	(23.2)	(26.8)
Impairment	0.0	(7.6)
Measurement period adjustments	0.6	0.9
Foreign currency translation	13.4	1.8
Ending balance	525.5	394.7	379.9
Intangible Asset and Goodwill
Goodwill [Roll Forward]
Dispositions of businesses	0.0	(41.8)
Contingent considerations	0.0	0.0
Measurement period adjustments	7.2	6.8
Finite-lived Intangible Assets [Roll Forward]
Acquisitions of businesses	140.0	99.4
Foreign currency translation	15.0	2.5
Amortization	(28.3)	(21.8)
Goodwill and Intangible Assets [Roll Forward]
Beginning balance	654.7	537.5
Write-off	(6.2)	(10.4)
Ending balance	782.4	654.7	$ 537.5
Intangible Asset and Goodwill | Renewal rights
Finite-lived Intangible Assets [Roll Forward]
Acquisitions of businesses	0.0	82.5
MediaAlpha
Goodwill [Roll Forward]
Dispositions of businesses		(18.3)
MediaAlpha | Total other intangible assets
Goodwill [Roll Forward]
Dispositions of businesses	0.0	(23.5)
Other Operations
Finite-lived Intangible Assets [Roll Forward]
Impairments	(0.4)	(0.4)
Goodwill and Intangible Assets [Roll Forward]
Goodwill, impairment loss	7.6	7.6
Fresh Insurance Services Group Limited
Finite-lived Intangible Assets [Roll Forward]
Impairments	(6.2)	(2.4)
KBK Insurance Group, Inc. & KBK Premium Services, Inc. | Goodwill
Goodwill [Roll Forward]
Contingent considerations	$ 4.1	$ 5.9

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- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Amount of foreign currency translation gain (loss) which increases (decreases) assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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