Income Taxes - Net operating loss carryforwards and Tax credit carryforwards (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)
Income Taxes
Net operating loss carryforwards	$ 38,186,000
Federal
Income Taxes
Net operating loss carryforwards	19,555,000
Research credit carryforwards | Federal
Income Taxes
Tax credit carryforwards	1,363,000
Research credit carryforwards | State
Income Taxes
Tax credit carryforwards	582,000
After tax year 2017 | Federal
Income Taxes
Net operating loss carryforwards	$ 16,450,000
Utilization of operating loss carryforwards of taxable income (as a percent)	80.00%