Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Income tax paid	$ 0	$ 0	$ 0
U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	151,400,000
Research and development tax credit	10,000,000
Foreign
Income Taxes [Line Items]
Net operating loss carryforwards	21,600,000
State and City
Income Taxes [Line Items]
Net operating loss carryforwards	65,500,000
Subject To Annual Limitations | U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	16,800,000
Not Subject To Annual Limitations | U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	116,800,000
Research and development tax credit	10,000,000
Not Subject To Annual Limitations | State and City
Income Taxes [Line Items]
Net operating loss carryforwards	$ 65,300,000