Significant Accounting Policies - Home Office and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Significant Accounting Policies [Line Items]
Accumulated depreciation of home office and equipment	$ 57.1	$ 55.4	$ 51.2
Depreciation expense of home office and equipment	$ 4.9	$ 5.6	$ 6.3
Minimum
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	3 years
Maximum
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	45 years