Income Taxes (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	$ 0.0	$ 0.0
Federal tax at statutory rate (as a percent)	21.00%	35.00%
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 110.9
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		65.9
R&D credit
Operating Loss Carryforwards [Line Items]
Credit carryforwards		$ 1.4