Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows provided by operating activities:
Net income (loss)	$ 6.7	$ (54.1)	$ (14.1)
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Amortization and depreciation	43.4	33.2	27.3
Share-based payments expense	8.0	8.7	16.9
Deferred income tax benefit, net	(38.6)	(21.6)	(23.5)
Net realized investment (gains) losses	(32.6)	3.6	(80.1)
Undistributed earnings from alternative investment portfolio	(95.5)	(8.6)	(19.9)
Loss on disposals of long-lived assets, net	23.3	5.5	7.2
Impairment of goodwill and intangibles	43.2	0.0	15.6
Change in:
Accrued investment income	0.8	3.9	1.5
Receivables	47.4	84.8	(455.1)
Deferred acquisition costs	0.8	(4.6)	7.0
Ceded unearned premiums	65.7	(33.2)	(87.8)
Reserves for losses and loss adjustment expenses	210.8	280.2	509.0
Unearned premiums	7.2	63.7	111.7
Ceded reinsurance payable and funds held	(207.3)	(238.2)	243.3
Income taxes	(4.5)	(17.5)	11.4
Accrued underwriting expenses and other liabilities	3.0	(43.7)	(10.6)
Other, net	17.9	9.8	(77.0)
Net cash flows from operating activities	99.7	71.9	182.8
Cash flows used in investing activities:
Sales of fixed maturity investments	992.9	1,080.0	1,394.3
Maturities and mandatory calls of fixed maturity investments	717.7	569.8	522.2
Sales of equity securities	125.8	25.4	374.7
Sales of other investments	212.3	103.9	83.1
Purchases of fixed maturity investments	(1,932.9)	(2,038.1)	(1,859.1)
Purchases of equity securities	(5.3)	(78.9)	(61.2)
Purchases of other investments	(47.4)	(35.5)	(63.7)
Change in foreign regulatory deposits and voluntary pools	(27.1)	(5.4)	0.0
Change in short-term investments	(116.4)	285.4	(490.4)
Settlements of foreign currency exchange forward contracts	(1.2)	9.4	0.3
Proceeds from sale of Ariel Re, net of cash transferred	0.0	28.3	0.0
Proceeds from sale of Trident assets	0.0	38.0	0.0
Sale (Purchases) of fixed assets, net	18.0	(20.2)	(29.9)
Other, net	7.7	13.6	(13.1)
Cash used in investing activities	(55.9)	(24.3)	(142.8)
Cash flows from financing activities:
Payment of long-term debt	0.0	(125.0)	(0.6)
Issuance of preferred shares, net of issuance costs	0.0	144.0	0.0
Activity under stock incentive plans	1.3	1.8	1.9
Payment of cash dividends to preferred shareholders	(10.5)	(4.6)	0.0
Payment of cash dividends to common shareholders	(43.7)	(43.0)	(43.1)
Cash used in financing activities	(52.9)	(26.8)	(41.8)
Effect of exchange rate changes on cash	6.4	(9.8)	(0.1)
Change in cash	(2.7)	11.0	(1.9)
Cash, beginning of year	148.8	137.8	139.7
Cash, end of period	$ 146.1	$ 148.8	$ 137.8