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Income Taxes - Additional Information (Detail)
 9 Months Ended
Sep. 30, 2018
USD ($)
Income Taxes [Line Items]  
Net deferred tax asset $ 0
Income tax expense 0
Valuation allowance, net operating loss $ 1,700,000
Estimated annual effective tax rate 25.00%
Effective tax rate 0.00%
U.S. federal tax rate 21.00%
Federal [Member]  
Income Taxes [Line Items]  
Net operating loss carryforwards $ 1,700,000
Net operating loss carryforwards subject to expiration $ 163,300,000
Net operating loss carryforwards expiration year 2025
Net operating loss carryforwards expiration year 2037
Foreign [Member]  
Income Taxes [Line Items]  
Net operating loss carryforwards $ 5,700,000
Net operating loss carryforwards subject to expiration $ 37,500,000