Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Increase in the valuation allowance	$ 5,500,000
Uncertain tax positions interest and penalties accrued	0	$ 0
Effect of remeasurement of deferred tax assets and liabilities under Tax Cuts and Jobs Act	3,700,000
Federal
Income Taxes [Line Items]
Net operating loss carryforward	24,500,000
State
Income Taxes [Line Items]
Net operating loss carryforward	21,300,000
Germany | Corporate Income Tax Carryforwards
Income Taxes [Line Items]
Net operating loss carryforward	46,100,000
Germany | Trade Tax Carryforwards
Income Taxes [Line Items]
Net operating loss carryforward	$ 45,600,000
Australia
Income Taxes [Line Items]
Australian tax credit from R&D activities		1,500,000
Income taxes receivable		$ 1,500,000