Consolidated Statements of (Loss) Income - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Premiums and other revenue:
Earned premiums	$ 1,729,500,000	$ 1,731,700,000	$ 1,572,300,000
Net investment income	151,100,000	133,100,000	140,000,000.0
Fee and other income	9,100,000	9,000,000.0	22,500,000
Net realized investment gains (losses):
Net realized investment gains	120,800,000	33,100,000	39,300,000
Change in fair value of equity securities	(40,800,000)	(105,100,000)	0
Net realized investment gains (losses)	80,000,000.0	(72,000,000.0)	39,300,000
Total revenue	1,969,700,000	1,801,800,000	1,774,100,000
Expenses:
Losses and loss adjustment expenses	1,220,700,000	1,040,800,000	1,050,200,000
Underwriting, acquisition and insurance expenses	665,800,000	654,700,000	635,400,000
Other corporate expenses	37,600,000	0	0
Interest expense	33,600,000	31,600,000	27,700,000
Fee and other expense	5,800,000	7,100,000	14,600,000
Foreign currency exchange (gains) loss	(9,600,000)	(100,000)	6,300,000
Impairment of goodwill	15,600,000	0	0
Total expenses	1,969,500,000	1,734,100,000	1,734,200,000
Income before income taxes	200,000	67,700,000	39,900,000
Income tax provision (benefit)	8,600,000	4,100,000	(10,400,000)
Net (loss) income	$ (8,400,000)	$ 63,600,000	$ 50,300,000
Net (loss) income per common share:
Basic (in dollars per share)	$ (0.25)	$ 1.87	$ 1.46
Diluted (in dollars per share)	(0.25)	1.83	1.42
Dividend declared per common share (in dollars per share)	$ 1.24	$ 1.08	$ 0.94
Weighted average common shares:
Basic (in shares)	34,205,954	33,922,009	34,457,098
Diluted (in shares)	34,205,954	34,678,781	35,371,644
Net realized investment gains (losses) before other-than-temporary impairment losses	$ 100,300,000	$ (64,400,000)	$ 41,800,000
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	(20,300,000)	(6,600,000)	(800,000)
Other-than-temporary impairment losses on equity securities	0	0	(1,700,000)
Other-than-temporary impairment losses on other invested assets	0	(1,000,000.0)	0
Impairment losses recognized in earnings	$ (20,300,000)	$ (7,600,000)	$ (2,500,000)