Annual report pursuant to Section 13 and 15(d)

Provision for Income Taxes - Additional Information (Detail)

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Provision for Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Taxes Disclosure [Line Items]    
Federal Statutory Rate 21.00% 34.00%
Operating loss carryforwards, limitations on use Net operating loss carryforwards generated after January 1, 2018 may be carried forward indefinitely, subject to the 80% taxable income limitation on the utilization of the carryforwards.  
Research and development credit carry forward $ 547 $ 490
Open tax year 2014  
Federal [Member]    
Income Taxes Disclosure [Line Items]    
Operating loss carry forward $ 122,300  
Operating loss carry forwards expiration year 2034  
Research and development credit carry forward $ 342  
Research and development credit expiration year 2036  
State [Member]    
Income Taxes Disclosure [Line Items]    
Operating loss carry forward $ 119,601  
Operating loss carry forwards expiration year 2019  
Research and development credit carry forward $ 260  
Maximum [Member]    
Income Taxes Disclosure [Line Items]    
Federal Statutory Rate   35.00%