Build-to-Suit Lease - Additional Information (Detail) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Aug. 01, 2018 USD ($)	Mar. 31, 2017 USD ($) ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Operating Leased Assets [Line Items]
Operating lease payments			$ 17,420	$ 17,420
Option to extend, existence, operating facility lease		true
Property and equipment, net			32	32	$ 798
Build-to-suit obligation			7,324	7,324	$ 5,428
Build-to-suit related to construction costs incurred				3,500
Assets Held under Operating Leases [Member]
Operating Leased Assets [Line Items]
Property and equipment, net			8,900	8,900
1020 Marsh Road, Menlo Park, California [Member]
Operating Leased Assets [Line Items]
Operating facility lease area | ft²		34,500
Operating facility lease term		86 months
Lease agreement, additional extended lease term		5 years
Tenant improvement allowance		$ 1,900
Letter of credit to secure lease obligations		2,400
Operating lease payments		$ 20,000	17,000	$ 17,000
Lease commencement date		August 2017
1020 Marsh Road, Menlo Park, California [Member] | Sublease Agreement [Member] | EVA Automation, Inc [Member]
Operating Leased Assets [Line Items]
Operating facility lease term	72 months
Lease commencement date	October 1, 2018
Abatement of base rent lease payment	$ 900
Operating lease abatement term	5 months
Operating lease payments receivable			$ 600
1060 Marsh Road [Member]
Operating Leased Assets [Line Items]
Operating facility lease area | ft²		17,400