Fair Value of Financial Instruments - Schedule of Inputs of the Black-Scholes Option Pricing Model (Details) - Black-Scholes option pricing model - Weichai Warrant liability - Level 3	Dec. 31, 2018 $ / shares	Dec. 31, 2017 $ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contractual term	6 months	1 year
Market value of the Common Stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Option pricing model input	9.25	7.5
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Option pricing model input	0.026	0.018
Estimated price volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Option pricing model input	0.55	0.95
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Option pricing model input	0	0