Segment Information (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Reconciliation of operating results by reportable segment

The following table presents operating results by reportable segment for the years ended:

	December 31, 2017								December 31, 2016								December 31, 2015
	Property & Casualty			Other		Total			Property & Casualty			Other		Total			Property & Casualty		Other		Total
	(Amounts in millions)
Net premiums earned	$	3,160.9		$	34.5	$	3,195.4		$	3,089.9		$	41.9	$	3,131.8		$	2,906.6	$	51.3	$	2,957.9
Less:
Losses and loss adjustment expenses	2,427.8			17.1		2,444.9			2,333.2			21.9		2,355.1			2,117.3		28.2		2,145.5
Underwriting expenses	773.1			15.6		788.7			780.4			17.5		797.9			770.0		20.0		790.0
Underwriting (loss) gain	(40.0		)	1.8		(38.2		)	(23.7		)	2.5		(21.2		)	19.3		3.1		22.4
Investment income						124.9								121.9							126.3
Net realized investment gains (losses)						83.7								(34.3		)					(83.8		)
Other income						11.9								8.3							8.9
Interest expense						(15.2		)						(4.0		)					(3.2		)
Pre-tax income						$	167.1							$	70.7						$	70.6
Net income						$	144.9							$	73.0						$	74.5

Schedule direct premiums attributable to segment

The following table presents the Company’s net premiums earned and direct premiums written by line of insurance business for the years ended:

	December 31, 2017						December 31, 2016						December 31, 2015
	Property & Casualty		Other		Total		Property & Casualty		Other		Total		Property & Casualty		Other		Total
	(Amounts in millions)
Private passenger automobile	$	2,473.8	$	—	$	2,473.8	$	2,435.7	$	—	$	2,435.7	$	2,308.6	$	—	$	2,308.6
Homeowners	431.6		—		431.6		414.0		—		414.0		379.7		—		379.7
Commercial automobile	171.9		—		171.9		161.3		—		161.3		144.4		—		144.4
Other	83.6		34.5		118.1		78.9		41.9		120.8		73.9		51.3		125.2
Net premiums earned	$	3,160.9	$	34.5	$	3,195.4	$	3,089.9	$	41.9	3,131.8		$	2,906.6	$	51.3	$	2,957.9
Private passenger automobile	$	2,480.0	$	—	$	2,480.0	$	2,452.7	$	—	$	2,452.7	$	2,345.8	$	—	$	2,345.8
Homeowners	469.9		—		469.9		436.9		—		436.9		402.2		—		402.2
Commercial automobile	178.2		—		178.2		166.1		—		166.1		153.5		—		153.5
Other	92.9		27.9		120.8		89.0		27.3		116.3		81.6		29.8		111.4
Direct premiums written	$	3,221.0	$	27.9	$	3,248.9	$	3,144.7	$	27.3	$	3,172.0	$	2,983.1	$	29.8	$	3,012.9