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Income Taxes -Additional Information (Detail) - USD ($)
$ in Thousands
 1 Months Ended 12 Months Ended
Aug. 31, 2004
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Taxes [Line Items]        
Amount Equity would be increased   $ 11,600    
Change in the valuation allowance   (48,100) $ 80,100 $ 65,500
Federal operating loss carryforwards   1,900,000    
State operating loss carryforwards   1,300,000    
Net operating loss carryforwards $ 216,000      
Net operating loss and credit carryforwards, annual use limitation $ 13,000      
Research and development credits   $ 77,998 $ 73,646  
Federal        
Income Taxes [Line Items]        
Net operating loss carryforwards, expiration year   2018    
Research and development credits   $ 53,000    
Federal research and development credits begin to expire   2024    
State        
Income Taxes [Line Items]        
Research and development credits   $ 38,500