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Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Jun. 28, 2019
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Significant Accounting Policies [Line Items]        
Reverse stock split 1-for-14      
Accumulated deficit   $ 320,551   $ 322,304
Cash, cash equivalents and available-for-sale investments   $ 49,800    
Shares used in computing diluted net income (loss) per share   6,884,797 2,418,674  
Restricted Stock Units [Member]        
Significant Accounting Policies [Line Items]        
Shares used in computing diluted net income (loss) per share   3,006    
Pangu BioPharma [Member] | Hong Kong [Member]        
Significant Accounting Policies [Line Items]        
Majority-owned subsidiary percentage   98.00%