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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Disclosure [Line Items]      
Provision for income taxes $ 0 $ 0 $ 0
Increase in valuation allowance 13,400,000 $ 3,000,000 $ 2,900,000
Research and development tax credit carryforwards, state 600,000    
Research and development tax credit carryforwards, federal $ 1,100,000    
Federal research and development tax credits, expiration start date 2035    
Earliest Tax Year [Member]      
Income Tax Disclosure [Line Items]      
Open tax year 2012    
Latest Tax Year [Member]      
Income Tax Disclosure [Line Items]      
Open tax year 2016    
Australian Taxation Office [Member]      
Income Tax Disclosure [Line Items]      
Accumulated tax losses carry forward $ 9,200,000    
Domestic Tax Authority [Member]      
Income Tax Disclosure [Line Items]      
Accumulated tax losses carry forward $ 48,000,000    
Net operating loss carryforwards expiration year 2033    
State and Local Jurisdiction [Member]      
Income Tax Disclosure [Line Items]      
Accumulated tax losses carry forward $ 37,700,000    
Net operating loss carryforwards expiration year 2033