Consolidated Statements of Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums and other revenue:
Earned premiums	$ 1,910.1	$ 1,780.5	$ 1,729.7
Net investment income	187.6	112.7	151.1
Net realized investment gains (losses):
Net realized investment gains (losses)	72.4	26.0	120.9
Change in fair value recognized	(40.4)	10.3	(40.8)
Credit losses on fixed maturities	0.6	(39.9)	0.0
Net realized investment gains (losses)	32.6	(3.6)	80.1
Total revenue	2,130.3	1,889.6	1,960.9
Expenses:
Losses and loss adjustment expenses	1,314.6	1,208.8	1,220.7
Underwriting, acquisition and insurance expenses	702.3	667.7	666.0
Non-operating expenses	43.7	21.1	37.6
Interest expense	21.6	26.9	34.1
Fee and other (income) expense, net	(2.0)	(3.9)	(3.3)
Foreign currency exchange (gains) losses	1.6	15.4	(9.8)
Impairment of goodwill and intangibles	43.2	0.0	15.6
Total expenses	2,125.0	1,936.0	1,960.9
Income (loss) before income taxes	5.3	(46.4)	0.0
Income tax provision (benefit)	(1.4)	7.7	14.1
Net income (loss)	6.7	(54.1)	(14.1)
Dividends on preferred shares	10.5	4.6	0.0
Net income (loss) attributable to common shareholders, diluted	(3.8)	(58.7)	(14.1)
Net income (loss) attributable to common shareholders, basic	$ (3.8)	$ (58.7)	$ (14.1)
Net loss attributable to common shareholders per common share:
Basic (in dollars per share)	$ (0.11)	$ (1.70)	$ (0.41)
Diluted (in dollars per share)	(0.11)	(1.70)	(0.41)
Dividend declared per common share (in dollars per share)	$ 1.24	$ 1.24	$ 1.24
Weighted average common shares:
Basic (in shares)	34,816,160	34,614,813	34,205,954
Diluted (in shares)	34,816,160	34,614,813	34,205,954
Other-than-temporary impairment losses recognized in earnings:
Net realized investment gains (losses) before other-than-temporary impairment losses	$ 32.6	$ (3.6)	$ 100.4
Other-than-temporary impairment losses on fixed maturities	0.0	0.0	(20.3)
Investment impairment losses recognized in earnings	$ 0.0	$ 0.0	$ (20.3)