Quarterly report pursuant to Section 13 or 15(d)

Commitments - Schedule of ROU Assets and Liabilities Related to Lease and First Lease Amendment (Detail)

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Commitments - Schedule of ROU Assets and Liabilities Related to Lease and First Lease Amendment (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Jan. 01, 2019
Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]      
ROU assets $ 436 $ 600  
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] us-gaap:OtherAssetsNoncurrent    
Current portion of lease liabilities $ 419   $ 0
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] us-gaap:OperatingLeaseLiabilityCurrent    
Lease liabilities, less current portion $ 116   $ 0
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] us-gaap:OperatingLeaseLiabilityNoncurrent    
Total lease liabilities $ 535 $ 700