Reinsurance - Premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Abstract]
Direct premiums	$ 870.3	$ 657.2	$ 88.9
Reinsurance assumed	0.0	0.0	0.1
Reinsurance ceded	(0.1)	(0.1)	(0.2)
Total premiums, net	$ 870.2	$ 657.1	$ 88.8