Leases - Additional Information (Detail)		1 Months Ended			12 Months Ended
	Aug. 31, 2020 USD ($) ft²	Oct. 31, 2018 ft²	Aug. 01, 2018 USD ($)	Mar. 31, 2017 ft² Lease	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jan. 01, 2019 USD ($)
Lessee Lease Description [Line Items]
Derecognized build-to-suit lease asset.									$ 8,600,000
Derecognized build-to-suit lease obligation.									7,300,000
Accumulated deficit					$ (500,654,000)	$ (470,111,000)			1,300,000
Operating lease right-of-use assets					2,958,000	8,697,000			10,400,000
leasehold improvement assets							$ 500,000	$ 500,000	2,200,000
Operating lease obligation					8,517,000				12,600,000
Derecognized deferred rent									$ 100,000
Number of lease renewal option | Lease				1
Cash paid for measurement of lease obligations for operating cash flows from operating leases					2,300,000	2,700,000
Rent expense					2,100,000	2,500,000
Short term and variable lease cost					$ 500,000	500,000
Weighted average remaining lease term					3 years 10 months 24 days
Weighted average discount rate					7.62%
Write-off lease receivable/prepaid commission assets					$ 1,383,000
1020 Marsh Road, Menlo Park, California [Member]
Lessee Lease Description [Line Items]
Operating facility lease area | ft²				34,500
Lease commencement date				2017-08
Operating facility lease term				87 months
Lease agreement, one renewal option term				5 years
1020 Marsh Road, Menlo Park, California [Member] | Sublease Agreement [Member] | EVA Automation, Inc [Member]
Lessee Lease Description [Line Items]
Operating facility lease term			72 months
Operating lease abatement term			5 months
Sublease commencement date			Oct. 01, 2018
Abatement of base rent lease payment			$ 900,000
Write-off lease receivable/prepaid commission assets					1,400,000
Operating lease sublease income (loss)					(13,000)	2,500
Cash received from sublease					$ 1,200,000	$ 2,300,000
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		2018-10
Lease expires date		Aug. 31, 2020
North Carolina [Member]
Lessee Lease Description [Line Items]
Operating facility lease area | ft²	4,128
Operating facility lease term	63 months
Operating lease abatement term	3 months
Cash paid for measurement of lease obligations for operating cash flows from operating leases	$ 9,000