Commitments and Contingencies - Additional Information (Details)		1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($)	Mar. 31, 2020 piece	Oct. 31, 2019 piece	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Lease term				36 months		36 months
Present value of annual rental payments including guaranteed residual value, percentage						90.00%
Lease buyout agreement, number of lab equipment | piece		2	2
Lease buyout agreement, remaining balance of lease liability				$ 0		$ 0
Future minimum payments required under capital leases				$ 0		$ 0
Operating lease, agreement term				5 years		5 years
Operating lease, renewal term				30 months		30 months
Operating lease, description						In July 2016, we entered into a five-year lease agreement for our headquarters facility located in Foster City, California. The term of the lease is from September 1, 2016 to August 31, 2021, with two 30-month renewal options.
Operating leases, rent expense recognized				$ 200,000	$ 200,000	$ 500,000	$ 400,000
Lonza DMSA
Loss Contingencies [Line Items]
Amount recorded with respect to the potential future payments above the initial cash cap				$ 0		$ 0		$ 0
Minimum
Loss Contingencies [Line Items]
Lease interest rate				6.90%		6.90%
Maximum
Loss Contingencies [Line Items]
Lease interest rate				15.00%		15.00%
Maximum | Lonza DMSA
Loss Contingencies [Line Items]
Payments in equity, percentage	25.00%
Payments in equity, amount	$ 2,500,000
Equity payment, upper limit	$ 10,000,000