Commitments and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended			9 Months Ended
	Mar. 31, 2017 USD ($) ft² Lease	Dec. 31, 2015 ft²	Mar. 31, 2014 ft²	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Number of lease renewal option | Lease	1
Operating lease payments				$ 20,312
Build-to-suit obligation				5,428
Property and equipment, net				861	$ 265
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				$ 8,900
Menlo Park, California [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²			12,900
Operating facility lease term			39 months
Lease expiration end date			2017-08
Operating lease payments	$ 20,000
Menlo Park, California [Member] | Sublease Agreement [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²		10,900
Operating facility lease term		24 months
Lease commencement date				Jan. 01, 2016
Total obligation under lease				$ 300
1020 Marsh Road, Menlo Park, California [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²	34,500
Operating facility lease term	86 months
Lease facility delivery date	2017-04
Lease commencement date	August 8, 2017
Lease agreement, one renewal option term	5 years
Operating lease payments				$ 20,000
Tenant improvement allowance	$ 1,900
Letter of credit to secure lease obligations	$ 2,400
Lease facility began occupying date	2017-08
Lease agreement, additional extended lease term	5 years
1060 Marsh Road [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²	17,400