Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Segments shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares shares	Jan. 01, 2018 USD ($)
Organization and Summary of Significant Accounting Policies [Line Items]
Liquid investments purchased with original maturities	three months or less
Percentage of likelihood of indefinite lived intangible assets being impaired	50.00%
Percentage of likelihood of income tax examination favourable settlement being realized	50.00%
Stock options and RSUs outstanding | shares	9,048,793	8,367,628	9,578,322
Number of operating segments | Segments	1
Accumulated deficit	$ (562,696)	$ (495,479)
Restricted cash	3,500	$ 3,500
Brisbane Build-to-Suit Lease [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Restricted cash	3,500
ASU No. 2014-09 [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Accumulated deficit				$ (494,362)
ASU No. 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Accumulated deficit	$ (14,674)			1,117
ASU 2016-18 [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Restricted cash balance				$ 3,500
Bioverativ Inc [Member] | Customer Concentration Risk [Member] | Total revenues [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Percentage of revenues		34.00%	46.00%
Bioverativ Inc [Member] | Collaboration Contract Performance Period
Organization and Summary of Significant Accounting Policies [Line Items]
Increase in basic net loss per share | $ / shares			$ 0.06
Decrease in revenues			$ 4,300
Pfizer [Member] | Customer Concentration Risk [Member] | Total revenues [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Percentage of revenues	45.00%	47.00%
Kite Pharma, Inc. ("Kite") [Member] | Customer Concentration Risk [Member] | Total revenues [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Percentage of revenues	30.00%
Dow Agro Sciences [Member] | Customer Concentration Risk [Member] | Total revenues [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Percentage of revenues			26.00%
Shire AG [Member] | Customer Concentration Risk [Member] | Total revenues [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Percentage of revenues			17.00%
Minimum [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Estimated useful lives of related assets	3 years
Maximum [Member]
Organization and Summary of Significant Accounting Policies [Line Items]
Estimated useful lives of related assets	5 years