Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024
Cash Flows From Operating Activities
Net income	$ 285.3	$ 156.0
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized and unrealized investment losses	20.6	29.2
Net amortization and depreciation	(2.1)	1.6
Stock-based compensation expense	17.8	14.8
Amortization of defined benefit plan costs	3.3	3.4
Deferred income tax benefit	(2.5)	(5.2)
Change in deferred acquisition costs	(11.7)	(13.9)
Change in premiums receivable, net of reinsurance premiums payable	(81.7)	(113.2)
Change in loss, loss adjustment expense and unearned premium reserves	225.6	220.1
Change in reinsurance recoverable	15.6	18.6
Change in expenses and taxes payable	(150.2)	(59.9)
Other, net	(74.5)	(53.3)
Net cash provided by operating activities	245.5	198.2
Cash Flows From Investing Activities
Proceeds from disposals and maturities of fixed maturities	1,476.4	1,100.2
Proceeds from disposals of equity securities and other investments	57.8	34.5
Purchase of fixed maturities	(1,818.9)	(1,204.3)
Purchase of equity securities and other investments	(46.2)	(34.4)
Capital expenditures	(3.5)	(4.8)
Net cash used in investing activities	(334.4)	(108.8)
Cash Flows From Financing Activities
Proceeds from exercise of employee stock options	12.2	6.9
Dividends paid to shareholders	(64.7)	(61.1)
Repurchases of common stock	(38.6)	0.0
Other financing activities	(11.7)	(9.8)
Net cash used in financing activities	(102.8)	(64.0)
Net change in cash and cash equivalents	(191.7)	25.4
Net change in cash related to discontinued operations	0.3	(3.9)
Cash and cash equivalents, beginning of period	435.5	316.1
Cash and cash equivalents, end of period	$ 244.1	$ 337.6