Fair Value Measurement - Assumptions Used for Determining Fair Values of Common Stock Warrants (Detail)	Sep. 30, 2018 $ / shares	Sep. 20, 2018 $ / shares	Jan. 30, 2018 $ / shares
Warrant Fair Value Black Scholes Method [Line Items]
Beginning stock price		$ 3.285	$ 13.50
January 30, 2018 Offering [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Beginning stock price	$ 10.17
January 30, 2018 Offering [Member] | Exercise Price [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	4.53
January 30, 2018 Offering [Member] | Expected Dividend Yield [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	0.00
January 30, 2018 Offering [Member] | Discount Rate-Bond Equivalent Yield [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	2.48
January 30, 2018 Offering [Member] | Expected Life [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Expected life (in years)	5 years
January 30, 2018 Offering [Member] | Expected Volatility [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	99.00
August 13, 2018 Rights Offering [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Beginning stock price	$ 3.89
August 13, 2018 Rights Offering [Member] | Exercise Price [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	4.53
August 13, 2018 Rights Offering [Member] | Expected Dividend Yield [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	0.00
August 13, 2018 Rights Offering [Member] | Discount Rate-Bond Equivalent Yield [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	2.75
August 13, 2018 Rights Offering [Member] | Expected Life [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Expected life (in years)	5 years
August 13, 2018 Rights Offering [Member] | Expected Volatility [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	128.69
September 20, 2018 Offering [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Beginning stock price	$ 2.92
September 20, 2018 Offering [Member] | Exercise Price [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	3.16
September 20, 2018 Offering [Member] | Expected Dividend Yield [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	0.00
September 20, 2018 Offering [Member] | Discount Rate-Bond Equivalent Yield [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	2.77
September 20, 2018 Offering [Member] | Expected Life [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Expected life (in years)	5 years 6 months
September 20, 2018 Offering [Member] | Expected Volatility [Member]
Warrant Fair Value Black Scholes Method [Line Items]
Fair value measurement input	130.7