Income Taxes - Carryforwards (Details) $ in Millions	Dec. 31, 2018 USD ($)
U.S. state
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 21.5
Income tax credit carryforwards	1.0
China
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	0.5
U.S. Federal
Operating Loss Carryforwards [Line Items]
Income tax credit carryforwards	$ 0.0