Organization and Summary of Significant Accounting Policies - Revenues from Strategic Partnering Collaboration Agreements and Research Activity Grants (Detail) - Revenue from Contract with Customer - Revenue From Collaboration Agreements, Grants And Licensing Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pfizer
Concentration Risk [Line Items]
Percentage of revenues	40.00%	47.00%	47.00%
Kite Pharma, Inc. ("Kite")
Concentration Risk [Line Items]
Percentage of revenues	34.00%	30.00%
Sanofi
Concentration Risk [Line Items]
Percentage of revenues	22.00%	16.00%	34.00%