Commitments and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended				9 Months Ended
	Aug. 01, 2018 USD ($)	May 31, 2018 USD ($)	Jan. 31, 2018 USD ($)	Mar. 31, 2017 USD ($) ft² Lease	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Number of lease renewal option | Lease				1
Operating lease payments					$ 17,712
Inducement payment received					1,896
Build-to-suit obligation					7,324	$ 5,428
Property and equipment, net						$ 798
Build-to-suit related to construction costs incurred					3,500
Other potential commitments					10,000
Maximum [Member]
Loss Contingencies [Line Items]
Commitment to make development and sales-related milestone payments					30,000
Assets Held under Operating Leases [Member]
Loss Contingencies [Line Items]
Property and equipment, net					8,700
1020 Marsh Road, Menlo Park, California [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²				34,500
Lease facility delivery date				2017-04
Lease commencement date				August 8, 2017
Operating facility lease term				86 months
Lease agreement, one renewal option term				5 years
Operating lease payments				$ 20,000	$ 17,700
Tenant improvement allowance				1,900
Letter of credit to secure lease obligations				$ 2,400
Tenant improvement allowance received		$ 400	$ 1,500
Percentage of tenant improvement allowance received		20.00%	80.00%
Lease facility began occupying date				2017-08
Lease agreement, additional extended lease term				5 years
1020 Marsh Road, Menlo Park, California [Member] | Sublease Agreement [Member] | EVA Automation, Inc [Member]
Loss Contingencies [Line Items]
Lease commencement date	October 1, 2018
Operating facility lease term	72 months
Operating lease payments receivable	$ 14,700
Abatement of base rent lease payment	$ 900
Operating lease abatement term	5 months
1060 Marsh Road [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²				17,400