Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2014	Dec. 31, 2019
Income Tax Holiday [Line Items]
Unrecognized tax benefits				$ 0
Net operating loss carryforwards	$ 59,126,000			71,270,000
Valuation allowance, deferred tax asset, increase (decrease), amount	14,600,000	$ 18,500,000
Income tax holiday term			10 years
Research and development credits	5,780,000			6,586,000
Accrued interest related to uncertain tax positions				$ 0
State and Local Jurisdiction
Income Tax Holiday [Line Items]
Operating loss carryforwards	256,500,000
Research and development credits	3,000,000.0
Domestic Tax Authority
Income Tax Holiday [Line Items]
Operating loss carryforwards	262,200,000
Operating loss carryforwards, carried forward indefinitely	99,700,000
Research and development credits	$ 4,200,000