Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Contingently Issuable Warrants with option pricing model (Detail)

v3.19.1
Fair Value Measurements - Contingently Issuable Warrants with option pricing model (Detail) - Caelum Warrant Liabilities [Member]
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Measurement Input, Risk Free Interest Rate [Member] | Minimum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Risk-free interest rate   2.905%
Measurement Input, Risk Free Interest Rate [Member] | Maximum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Risk-free interest rate   2.909%
Measurement Input, Expected Dividend Rate [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Expected dividend yield 0.00% 0.00%
Measurement Input, Expected Term [Member] | Minimum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Expected term in years   3 years 10 months 2 days
Measurement Input, Expected Term [Member] | Maximum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Expected term in years   3 years 11 months 15 days
Measurement Input, Price Volatility [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Expected volatility   70.00%