Commitments and Contingencies - Additional Information (Details) $ in Thousands		3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 16, 2020 USD ($) ft²	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) officer	Sep. 01, 2020 ft²	Jun. 30, 2020 USD ($)	Aug. 31, 2015 ft²
Commitments And Contingencies [Line Items]
Rentable square feet of facility space | ft²										51,000
Optional term of extending lease agreement										5 years
Rent expense associated with primary facility lease (Topic 842)		$ 53		$ 225	$ 448	$ 655
February 2020 Restructuring
Commitments And Contingencies [Line Items]
Accrued severance costs		$ 0			0
Employee severance costs expensed			$ 59
Two Former Officers
Commitments And Contingencies [Line Items]
Number of former officers | officer							2
Severance expenses					0	$ 878
Accrued severance costs							$ 33
Primary Facility Lease
Commitments And Contingencies [Line Items]
Rentable square feet of facility space | ft²	12,000							10,000
Remaining minimum lease payments under Primary Facility Lease									$ 7,900
Lease termination expense	$ 600
Security deposit forfeited	539
Cash paid for lease termination fee.	61
Real estate broker fee	$ 405
Costs directly associated with execution of lease termination agreement.					1,005
Primary Facility Lease | Research and development
Commitments And Contingencies [Line Items]
Facility decommissioning and environmental remediation costs					$ 300