Michigan and Pennsylvania Operations (Details) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 29, 2016 employee	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Restructuring Cost and Reserve [Line Items]
Net premiums earned		$ 779.3	$ 731.6	$ 1,546.4	$ 1,452.3
Michigan And Pennsylvania [Member]
Restructuring Cost and Reserve [Line Items]
Net premiums earned						$ 15.4	$ 18.6
Combined ratio						137.00%	130.00%
Michigan And Pennsylvania [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Number of employees impacted by workforce reduction | employee	100
Expected employee termination costs		$ 2.0		$ 2.0