Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash Flows from Operating Activities:
Net Income (Loss)	$ (14,700,000)	$ 312,400,000
Adjustments to Reconcile Net Income (Loss) to Net Cash Provided by Operating Activities:
Net Realized Investment (Gains) Losses	(43,100,000)	(38,200,000)
Impairment Losses	7,800,000	20,000,000.0
Depreciation and Amortization of Property, Equipment and Software	32,800,000	26,600,000
Amortization of Intangibles Assets Acquired	46,400,000	14,100,000
(Increase) Decrease in Value of Equity and Convertible Securities	(92,400,000)	1,000,000.0
Receivables from Policyholders	(137,700,000)	(132,200,000)
Reinsurance Recoverables	24,400,000	13,800,000
Deferred Policy Acquisition Costs	(87,300,000)	(40,500,000)
Insurance Reserves	429,800,000	(10,300,000)
Unearned Premiums	172,900,000	136,100,000
Income Taxes	(121,500,000)	22,000,000.0
Other Assets and Liabilities	94,200,000	(79,100,000)
Net Cash Provided by Operating Activities	307,600,000	251,300,000
Cash Flows from Investing Activities:
Proceeds from Sales, Calls and Maturities of Fixed Maturities	1,015,600,000	707,000,000.0
Proceeds from Sale of Equity Securities, FV-NI	139,700,000	436,500,000
Proceeds from the Sales or Paydowns of Investments:
Real Estate Investments	6,200,000	5,400,000
Mortgage Loans	53,100,000	18,600,000
Other Investments	39,700,000	26,500,000
Purchases of Investments:
Fixed Maturities	(1,322,200,000)	(1,009,700,000)
Payments to Acquire Equity Securities, FV-NI	106,000,000.0	324,400,000
Real Estate Investments	(3,600,000)	(500,000)
Company-Owned Life Insurance	(100,000,000.0)	(100,000,000.0)
Mortgage Loans	(94,000,000.0)	(22,700,000)
Other Investments	(92,100,000)	(17,900,000)
Net Sales (Purchases) of Short-term Investments	715,100,000	(147,900,000)
Payments to Acquire Businesses, Net of Cash Acquired	(316,600,000)	0
Acquisition of Software and Long-lived Assets	(43,900,000)	(46,200,000)
Other	10,000,000.0	6,000,000.0
Net Cash Provided by (Used in) Investing Activities	(99,000,000.0)	(469,300,000)
Cash Flows from Financing Activities:
Repayment of Long-term Debt	(50,000,000.0)	0
Net Proceeds from Issuance of Long-term Debt	0	395,600,000
Proceeds from Policyholder Obligations	298,100,000	391,800,000
Repayment of Policyholder Obligations	(328,100,000)	(192,400,000)
Proceeds from Shares Issued under Employee Stock Purchase Plan	3,900,000	3,100,000
Common Stock Repurchases	(161,700,000)	(110,400,000)
Dividends and Dividend Equivalents Paid	(60,800,000)	(59,300,000)
Other	3,700,000	5,000,000.0
Net Cash (Used in) Provided by Financing Activities	(294,900,000)	433,400,000
Increase (Decrease) in Cash	(86,300,000)	215,400,000
Cash, Beginning of Year	206,100,000	136,800,000
Cash, End of Period	119,800,000	352,200,000
Equity Method Limited Liability Investments
Adjustments to Reconcile Net Income (Loss) to Net Cash Provided by Operating Activities:
Income (Loss) from Equity Method Investments	50,900,000	(5,600,000)
Alternative Energy Partnership Investments
Adjustments to Reconcile Net Income (Loss) to Net Cash Provided by Operating Activities:
Income (Loss) from Equity Method Investments	$ (46,900,000)	$ 0