Commitments and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended			3 Months Ended
	Mar. 31, 2017 USD ($) ft²	Dec. 31, 2015 ft²	Mar. 31, 2014 ft²	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Operating lease payments	$ 32,956			$ 32,956
Build-to-suit obligation	8,174			8,174
Property and equipment, net	8,386			8,386	$ 265
Assets Held under Operating Leases [Member]
Loss Contingencies [Line Items]
Property and equipment, net	8,200			8,200
Menlo Park, California [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²			12,900
Operating facility lease term			39 months
Total obligation under lease	300			300
Operating lease payments	32,200			32,200
Menlo Park, California [Member] | Sublease Agreement [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²		10,900
Operating facility lease term		24 months
Total obligation under lease	$ 400			$ 400
Lease commencement date				Jan. 01, 2016
1020 Marsh Road, Menlo Park, California [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²	34,500
Operating facility lease term	93 months
Lease facility anticipated delivery date	2017-04
Lease agreement, description				The initial term of the Lease is 93 months commencing on the date that is 120 days after the 1020 Space is delivered, with one renewal option for a five-year term. We have the option to terminate the lease with respect to the 1060 Space by so notifying Landlord on or before October 31, 2017, in which event the term of the Lease with respect to the 1020 Space will be reduced to 86 months.
Lease agreement, one renewal option term	5 years
Operating facility contingent lease term	86 months
Base rent expense per month	$ 200
Annual increase in base rent (as a percent)	3.00%
Tenant improvement allowance	$ 1,900			$ 1,900
Lease facility expected occupy date	2017-08
1060 Marsh Road [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²	17,400
Operating facility lease term	93 months
Lease facility anticipated delivery date	2017-11
Lease agreement, description				The initial term of the Lease is 93 months commencing on the date that is 120 days after the 1020 Space is delivered, with one renewal option for a five-year term. We have the option to terminate the lease with respect to the 1060 Space by so notifying Landlord on or before October 31, 2017, in which event the term of the Lease with respect to the 1020 Space will be reduced to 86 months.
Lease agreement, one renewal option term	5 years
Lease agreement optional termination date	Oct. 31, 2017
Base rent expense per month	$ 100
Annual increase in base rent (as a percent)	3.00%
Tenant improvement allowance	$ 1,000			$ 1,000
Lease facility expected occupy date	2018-02
1020 Space and the 1060 Space [Member]
Loss Contingencies [Line Items]
Letter of credit to secure lease obligations	$ 2,400			2,400
Increased letter of credit on termination of 1060 space lease	$ 3,600			$ 3,600