Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash Flows From Operating Activities
Net income (loss)	$ 115.5	$ (12.0)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Net realized and unrealized investment (gains) losses	(5.5)	22.8
Net amortization and depreciation	0.8	2.2
Stock-based compensation expense	6.7	7.1
Amortization of defined benefit plan costs	1.7	2.0
Deferred income tax expense (benefit)	1.1	(7.7)
Change in deferred acquisition costs	1.5	7.0
Change in premiums receivable, net of reinsurance premiums payable	(36.6)	6.8
Change in loss, loss adjustment expense and unearned premium reserves	24.9	145.6
Change in reinsurance recoverable	56.3	(8.2)
Change in expenses and taxes payable	(89.6)	(114.0)
Other, net	(18.1)	(33.5)
Net cash provided by operating activities	58.7	18.1
Cash Flows From Investing Activities
Proceeds from disposals and maturities of fixed maturities	213.8	171.7
Proceeds from disposals of equity securities and other investments	17.9	7.8
Purchase of fixed maturities	(289.5)	(259.2)
Purchase of equity securities and other investments	(14.4)	(23.3)
Capital expenditures	(2.6)	(3.5)
Net cash used in investing activities	(74.8)	(106.5)
Cash Flows From Financing Activities
Proceeds from exercise of employee stock options	4.2	3.0
Dividends paid to shareholders	(30.5)	(28.9)
Other financing activities	(9.1)	(9.2)
Net cash used in financing activities	(35.4)	(35.1)
Net change in cash and cash equivalents	(51.5)	(123.5)
Cash and cash equivalents, beginning of period	316.1	305.0
Cash and cash equivalents, end of period	$ 264.6	$ 181.5