Common Stock - Additional Information (Detail) - USD ($) | Feb. 28, 2017 | Jul. 31, 2018 | Jun. 30, 2018 | Mar. 31, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017 | May 19, 2017 | Mar. 30, 2014 |
Class of Stock [Line Items] | | | | | | | | | |
Net proceeds from issuance of common stock | | | | | $ 15,255,000 | $ 3,584,000 | | | |
Common stock, value, issued | | | | | $ 41,000 | | $ 36,000 | | |
Common stock, shares, issued | | | | | 41,136,738 | | 35,789,388 | | |
Private Placement 2017 | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Shares of common stock issued | 102,368 | | | | | | | | |
Proceeds from sale of common stock | $ 200,000 | | | | | | | | |
Warrants issued | 76,776 | | | | | | | | |
Issuance of warrants, price per share | $ 5 | | | | | | | | |
Issuance of warrants, value | $ 101,000 | | | | | | | | |
Issuance of warrants, closing price | $ 1.86 | | | | | | | | |
Warrants expiration date | | | | | Feb. 28, 2024 | | | | |
Private Placement 2017 | Measurement Input, Expected Term | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Warrants and rights outstanding, term | 7 years | | | | | | | | |
Private Placement 2017 | Measurement Input, Price Volatility | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Warrants and rights outstanding, measurement input percentage | 97.00% | | | | | | | | |
Private Placement 2017 | Measurement Input, Risk Free Interest Rate | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Warrants and rights outstanding, measurement input percentage | 1.92% | | | | | | | | |
2014 At Market Agreement | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Aggregate offering price | | | | | | | | | $ 30,000,000 |
Commission to sales agent as a percentage of gross proceeds | | | | | | | | | 3.00% |
Shares of common stock issued | | | | 1,496,797 | | | | | |
Net proceeds from issuance of common stock | | | | $ 1,945,000 | | | | | |
2017 At Market Agreement | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Aggregate offering price | | | | | | | | $ 30,000,000 | |
Commission to sales agent as a percentage of gross proceeds | | | | | | | | 3.00% | |
Shares of common stock issued | | 51,100 | 618,614 | | | | | | |
Net proceeds from issuance of common stock | | $ 362,000 | $ 5,241,000 | | | | | | |
Other Agreements | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Warrants issued | | | | | 290 | | | | |
Other Agreements | Series A, B and C Preferred Stock | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Common stock issued for dividend | | | | | 166,072 | | | | |
Other Agreements | Vendor | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Common stock, shares, issued | | | | | 2,883 | | | | |
Other Agreements | Maximum | Vendor | | | | | | | | | |
Class of Stock [Line Items] | | | | | | | | | |
Common stock, value, issued | | | | | $ 100,000 | | | | |