Commitments and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended		3 Months Ended
	Jan. 31, 2018 USD ($)	Mar. 31, 2017 USD ($) ft² Lease	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Number of lease renewal option | Lease		1
Operating lease payments			$ 18,749
Inducement payment received			1,516
Build-to-suit obligation			6,944	$ 5,428
Property and equipment, net			739	$ 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			8,800
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	$ 18,700
Tenant improvement allowance		1,900
Letter of credit to secure lease obligations		$ 2,400
Tenant improvement allowance received	$ 1,500
Percentage of tenant improvement allowance received	80.00%
Percentage of tenant improvement allowance expected to be received			20.00%
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