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Fair Value Measurements - Additional Information (Detail)
6 Months Ended
Jun. 30, 2018
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Long-term debt $ 6,900,000
Transfer of assets and liabilities between levels 0
Fair Value, Measurements, Nonrecurring [Member]  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Assets fair value on nonrecurring basis 0
Liabilities fair value on nonrecurring basis $ 0
Hercules Capital, Inc., [Member] | Secured Loan Agreement [Member] | Warrants [Member]  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Risk free rate 2.73%
Expected volatility 53.00%
Expected term 5 years 1 month 2 days