Fair Value Measurements - Assumptions (Details)	Mar. 31, 2020 $ / shares USD ($)	Sep. 30, 2019 $ / shares USD ($)
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant inputs	0.37	1.56
Remaining contractual life of warrant
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant inputs	4.88	5.38
Remaining contractual life of warrant | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Redemption feature input	1
Remaining contractual life of warrant | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Redemption feature input	2
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant inputs	90.2	89.0
Redemption feature input	130
Annual dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant inputs	0	0
Fair value of common stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant inputs | $ / shares	0.60	1.49