Subsequent Event (Details) $ in Thousands		3 Months Ended		12 Months Ended
	Apr. 29, 2016 USD ($) employee	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Subsequent Event [Line Items]
Net premiums earned		$ 767,100	$ 720,700	$ 767,100	$ 720,700
Michigan And Pennsylvania [Member]
Subsequent Event [Line Items]
Net premiums written				14,413	18,375
Net premiums earned				$ 15,366	$ 18,573
Combined ratio				137.00%	130.00%
Michigan And Pennsylvania [Member] | Subsequent Event [Member] | Employee Severance [Member]
Subsequent Event [Line Items]
Number of employees impacted by workforce reduction | employee	100
Expected employee termination costs	$ 2,000