Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash Flows From Operating Activities
Net income	$ 116.0	$ 418.7	$ 358.7
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on repayment of debt			6.2
Net realized investment (gains) losses	106.5	(123.0)	(5.0)
Net amortization and depreciation	12.9	16.9	18.2
Stock-based compensation expense	29.0	22.9	20.1
Amortization of defined benefit plan costs	5.5	3.4	6.0
Deferred income tax expense (benefit)	(46.5)	23.9	(23.0)
Change in deferred acquisition costs	(52.8)	(74.5)	(10.2)
Change in premiums receivable, net of reinsurance premiums payable	(116.7)	(123.4)	(84.0)
Change in loss, loss adjustment expense and unearned premium reserves	784.7	677.0	437.9
Change in reinsurance recoverable	(57.2)	(32.9)	(60.0)
Change in expenses and taxes payable	3.3	179.0	67.5
Other, net	(62.3)	(163.8)	(24.7)
Net cash provided by operating activities	722.3	823.7	707.6
Cash Flows From Investing Activities
Proceeds from disposals and maturities of fixed maturities	1,106.3	1,564.4	1,317.5
Proceeds from disposals of equity securities and other investments	488.4	286.3	172.8
Purchase of fixed maturities	(1,960.2)	(2,112.7)	(1,829.1)
Purchase of equity securities and other investments	(124.3)	(190.2)	(255.1)
Capital expenditures	(17.8)	(8.0)	(14.9)
Net cash used in investing activities	(507.6)	(460.2)	(608.8)
Cash Flows From Financing Activities
Proceeds from exercise of employee stock options	13.3	20.5	6.3
Proceeds from debt borrowings, net			296.4
Dividends paid to shareholders	(108.9)	(102.2)	(99.5)
Repayment of debt			(175.8)
Repurchases of common stock	(30.8)	(162.6)	(212.8)
Other financing activities	(14.2)	(8.9)	(8.5)
Net cash used in financing activities	(140.6)	(253.2)	(193.9)
Net change in cash and cash equivalents	74.1	110.3	(95.1)
Cash and cash equivalents, beginning of year	230.9	120.6	215.7
Cash and cash equivalents, end of year	305.0	230.9	120.6
Supplemental Cash Flow Information
Interest payments	33.3	33.4	33.9
Income tax payments, net	107.8	74.0	97.0
Continuing Operations [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized investment (gains) losses	$ 106.4	$ (123.5)	$ (5.1)