Investments - Net Realized Gains (Losses) Recognized in the Statement of Operations (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net realized gains (losses) related to sales:
Net realized gains (losses) from sales of fixed maturity securities	$ 0.2	$ 0.1	$ 0.0

Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

No definition available.

Name:	us-gaap_MarketableSecuritiesRealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration