Condensed Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Premiums and other revenue:
Earned premiums	$ 417.7	$ 399.1	$ 832.4	$ 778.5
Net investment income	33.2	43.6	69.2	74.1
Fee and other income	1.9	3.8	3.9	7.4
Net realized investment gains (losses):
Net realized investment gains	6.2	4.5	21.4	19.1
Change in fair value of equity securities	4.3	0.0	(26.6)	0.0
Net realized investment gains (losses)	10.5	4.5	(5.2)	19.1
Total revenue	463.3	451.0	900.3	879.1
Expenses:
Losses and loss adjustment expenses	245.5	230.6	482.7	453.1
Underwriting, acquisition and insurance expenses	156.8	154.7	317.0	308.3
Interest expense	7.8	7.0	15.5	12.9
Fee and other expense	1.6	3.3	3.6	7.4
Foreign currency exchange (gains) losses	(5.5)	4.6	(0.6)	3.9
Total expenses	406.2	400.2	818.2	785.6
Income before income taxes	57.1	50.8	82.1	93.5
Income tax provision	15.3	4.8	15.5	10.8
Net income	$ 41.8	$ 46.0	$ 66.6	$ 82.7
Net income per common share:
Basic (in dollars per share)	$ 1.23	$ 1.32	$ 1.96	$ 2.39
Diluted (in dollars per share)	1.20	1.29	1.92	2.32
Dividend declared per common share (in dollars per share)	$ 0.27	$ 0.23	$ 0.54	$ 0.47
Weighted average common shares:
Basic (in shares)	33,938,509	34,731,866	33,903,809	34,643,594
Diluted (in shares)	34,668,918	35,705,484	34,704,811	35,644,640
Net realized investment gains (losses) before other-than-temporary impairment losses	$ 11.4	$ 5.6	$ (3.3)	$ 20.6
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	(0.9)	0.0	(1.9)	0.0
Other-than-temporary impairment losses on equity securities	0.0	(1.1)	0.0	(1.5)
Impairment losses recognized in earnings	(0.9)	(1.1)	(1.9)	(1.5)
Net realized investment gains (losses)	$ 10.5	$ 4.5	$ (5.2)	$ 19.1