Consolidated Statements of Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums and other revenue:
Earned premiums	$ 1,740.4	$ 1,910.1	$ 1,780.5
Net investment income	129.8	187.6	112.7
Net investment and other gains (losses):
Net realized investment and other gains (losses)	(115.9)	72.4	26.0
Change in fair value recognized	3.1	(40.4)	10.3
Change in allowance for credit losses on fixed maturity securities	(2.5)	0.6	(39.9)
Total net investment and other gains (losses)	(115.3)	32.6	(3.6)
Total revenue	1,754.9	2,130.3	1,889.6
Expenses:
Losses and loss adjustment expenses	1,166.9	1,314.6	1,208.8
Underwriting, acquisition and insurance expenses	670.7	702.3	667.7
Non-operating expenses	51.5	43.7	21.1
Interest expense	26.8	21.6	26.9
Fee and other (income) expense, net	(1.3)	(2.0)	(3.9)
Foreign currency exchange (gains) losses	(5.0)	1.6	15.4
Impairment of goodwill and intangibles	28.5	43.2	0.0
Total expenses	1,938.1	2,125.0	1,936.0
Income (loss) before income taxes	(183.2)	5.3	(46.4)
Income tax provision (benefit)	(8.0)	(1.4)	7.7
Net income (loss)	(175.2)	6.7	(54.1)
Dividends on preferred shares	10.5	10.5	4.6
Net income (loss) attributable to common shareholders, diluted	(185.7)	(3.8)	(58.7)
Net income (loss) attributable to common shareholders, basic	$ (185.7)	$ (3.8)	$ (58.7)
Net income (loss) attributable to common shareholders per common share:
Basic (in dollars per share)	$ (5.31)	$ (0.11)	$ (1.70)
Diluted (in dollars per share)	(5.31)	(0.11)	(1.70)
Dividend declared per common share (in dollars per share)	$ 1.24	$ 1.24	$ 1.24
Weighted average common shares:
Basic (in shares)	34,980,608	34,816,160	34,614,813
Diluted (in shares)	34,980,608	34,816,160	34,614,813
Other-than-temporary impairment losses recognized in earnings:
Net realized investment gains (losses) before other-than-temporary impairment losses	$ (79.2)	$ 32.6	$ (3.6)
Other-than-temporary impairment losses on fixed maturities	(36.1)	0.0	0.0
Investment impairment losses recognized in earnings	$ (36.1)	$ 0.0	$ 0.0