Commitments and Contingencies, Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leases [Abstract]
Total expenses under operating lease obligations	$ 1.2	$ 1.2	$ 1.1
Office Space and Other Equipment
Operating Leases, Future Minimum Payments Due [Abstract]
2018	0.9
2019	0.9
2020	0.9
2021	0.8
2022	0.8
Thereafter	4.6
Total	$ 8.9