Leases - Additional Information (Detail) $ in Millions	1 Months Ended			3 Months Ended	9 Months Ended
	Oct. 31, 2018 ft²	Aug. 01, 2018 USD ($)	Mar. 31, 2017 ft² Lease	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Lessee Lease Description [Line Items]
Number of lease renewal option | Lease			1
Operating lease costs				$ 0.5	$ 1.6
Cash paid for measurement of lease obligations for operating cash flows from operating leases					$ 2.0
Weighted average remaining lease term				4 years 10 months 24 days	4 years 10 months 24 days
Weighted average discount rate				7.75%	7.75%
1020 Space [Member]
Lessee Lease Description [Line Items]
Operating facility lease area | ft²			34,500
Lease commencement date			August 2017
Operating facility lease term			87 months
Lease agreement, one renewal option term			5 years
1020 Space [Member] | Sublease Agreement [Member] | EVA Automation, Inc [Member]
Lessee Lease Description [Line Items]
Lease commencement date		October 1, 2018
Operating facility lease term		72 months
Abatement of base rent lease payment		$ 0.9
Operating lease abatement term		5 months
Operating lease payments receivable				$ 0.6	$ 1.9
Cash received from sublease					$ 1.4
2479 E. Bayshore Blvd, Palo Alto, California [Member] | Sublease Agreement [Member]
Lessee Lease Description [Line Items]
Operating facility lease area | ft²	4,240
Lease commencement date	October 2018
Lease expires date	Aug. 31, 2020