Catastrophe Reinsurance - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Catastrophe Claims [Line Items]
Catastrophic events classification by amount	$ 25,000,000.0
Ceded earned premiums	31,200,000	$ 27,400,000	$ 31,600,000
Incurred losses and LAE related to prior year (favorable) adverse development	36,400,000	(71,100,000)	(7,400,000)
Catastrophe
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	106,900,000	60,100,000	87,600,000
Incurred losses and LAE related to prior year (favorable) adverse development	200,000	(17,100,000)	(8,400,000)
Catastrophe | Life & Health Insurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	12,900,000	3,900,000	4,100,000
Incurred losses and LAE related to prior year (favorable) adverse development	500,000	800,000	100,000
Catastrophe | Specialty Property & Casualty Insurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	12,500,000	11,600,000	4,400,000
Incurred losses and LAE related to prior year (favorable) adverse development	200,000	500,000	(300,000)
Catastrophe | Preferred Property & Casualty Insurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	81,500,000	44,600,000	79,100,000
Incurred losses and LAE related to prior year (favorable) adverse development	(500,000)	(18,400,000)	(8,200,000)
Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	26,700,000	20,500,000	20,500,000
Catastrophe Reinsurance | Life & Health Insurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	1,200,000	100,000	100,000
Catastrophe Reinsurance | Specialty Property & Casualty Insurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	4,800,000	200,000	2,600,000
Catastrophe Reinsurance | Preferred Property & Casualty Insurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	20,700,000	20,200,000	17,800,000
Reinstatement Premium | Catastrophe Reinsurance | Property & Casualty Insurance Subsidiaries
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	0.0	0.0	400,000
Reinsurance Recoverable FHCF | Catastrophe
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	1,500,000	15,500,000	31,800,000
Reinsurance Recoverable FHCF | Catastrophe | Life & Health Insurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	$ 0.0	$ 1,600,000	$ 1,600,000