Common Stock - Additional Information (Detail) - USD ($)		1 Months Ended		3 Months Ended	9 Months Ended
	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	$ 5.00
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