Long-term Debt - Schedule of Unamortized Debt Issuance Costs Deducted from Carrying Value of Debt Liability (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Senior unsecured fixed rate notes	$ 143.8	$ 143.8
Less: unamortized debt issuance costs	(3.5)	(3.6)
Senior unsecured fixed rate notes, less unamortized debt issuance costs	$ 140.3	$ 140.2

Face (par) amount of debt instrument at time of issuance.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant