Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Premiums and other revenue:
Earned premiums	$ 1,731.7	$ 1,572.3	$ 1,410.8
Net investment income	133.1	140.0	115.1
Fee and other income	9.0	22.5	24.5
Net realized investment gains (losses):
Net realized investment gains	33.1	39.3	26.1
Change in fair value of equity securities	(105.1)	0.0	0.0
Net realized investment and other (losses) gains	(72.0)	39.3	26.1
Total revenue	1,801.8	1,774.1	1,576.5
Expenses:
Losses and loss adjustment expenses	1,040.8	1,050.2	810.1
Underwriting, acquisition and insurance expenses	654.7	635.4	547.0
Interest expense	31.6	27.7	19.6
Fee and other expense	7.1	14.6	22.4
Foreign currency exchange (gains) losses	(0.1)	6.3	(4.5)
Total expenses	1,734.1	1,734.2	1,394.6
Income before income taxes	67.7	39.9	181.9
Income tax provision (benefit)	4.1	(10.4)	35.2
Net income	$ 63.6	$ 50.3	$ 146.7
Net income per common share:
Basic (in dollars per share)	$ 1.87	$ 1.46	$ 4.23
Diluted (in dollars per share)	1.83	1.42	4.13
Dividend declared per common share (in dollars per share)	$ 1.08	$ 0.94	$ 0.75
Weighted average common shares:
Basic (in shares)	33,922,009	34,457,098	34,691,618
Diluted (in shares)	34,678,781	35,371,644	35,472,779
Net realized investment (losses) gains before other-than-temporary impairment losses	$ (64.4)	$ 41.8	$ 36.3
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	(6.6)	(0.8)	(1.7)
Other-than-temporary impairment losses on equity securities	0.0	(1.7)	(8.5)
Other-than-temporary impairment losses on other invested assets	(1.0)	0.0	0.0
Impairment losses recognized in earnings	$ (7.6)	$ (2.5)	$ (10.2)