Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Net premiums earned	$ 574.4	$ 615.3	$ 695.8
Net investment income	72.7	76.3	88.1
Net realized and unrealized gains on investments	54.6	19.0	51.1
Other income	1.4	0.8	0.9
Total revenues	703.1	711.4	835.9
Expenses
Losses and loss adjustment expenses	315.2	302.4	365.9
Commission expense	76.1	78.8	88.1
Underwriting and general and administrative expenses	160.2	181.3	187.5
Interest and financing expenses	0.5	0.4	0.6
Other expenses	4.1	0.8	0.0
Total expenses	556.1	563.7	642.1
Net income before income taxes	147.0	147.7	193.8
Income tax expense	27.7	27.9	36.7
Net income	119.3	119.8	157.1
Comprehensive income
Unrealized AFS investment gains (losses) during the period, net of tax (expense) benefit of $13.6, $(14.2), and $(21.8) for the years ended December 31, 2021, 2020, and 2019, respectively	(51.3)	53.4	82.1
Reclassification adjustment for realized AFS investment gains in net income, net of tax expense of $0.9, $0.9, and $0.8 for the years ended December 31, 2021, 2020, and 2019, respectively	(3.2)	(3.6)	(3.1)
Other comprehensive income (loss), net of tax	(54.5)	49.8	79.0
Total comprehensive income	64.8	169.6	236.1
Net realized and unrealized gains on investments
Marketable Securities, Gain (Loss), Excluding Other-than-temporary Impairment Loss	$ 54.6	$ 19.0	$ 51.1
Earnings per common share (Note 18):
Basic	$ 4.22	$ 4.01	$ 4.89
Diluted	4.17	3.97	4.83
Cash dividends declared per common share and eligible equity plan holders	$ 1.00	$ 1.00	$ 0.88