Income Taxes - Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2017 USD ($)
United States—Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 19.8
Operating loss carryforwards, limitations on use, 5 years	0.4
Operating loss carryforwards, limitations on use, 15 years	0.2
United States—State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	17.6
Operating loss carryforwards, limitations on use, 20 years	$ 0.1