Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended	9 Months Ended
	Aug. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Class Of Stock [Line Items]
Net proceeds from sale of common stock		$ 5,603,000	$ 36,907,000
ATM Program | Cowen and Company LLC
Class Of Stock [Line Items]
Common stock value remained available for sale		$ 42,500,000
ATM Program | Cowen and Company LLC | Common Stock
Class Of Stock [Line Items]
Aggregate maximum offering price	$ 50,000,000
Number of shares issued and sold		1,201,464
Shares sold, average price per share		$ 4.89
Gross proceeds from sale of common stock		$ 5,900,000
Net proceeds from sale of common stock		$ 5,600,000
ATM Program | Maximum | Cowen and Company LLC | Common Stock
Class Of Stock [Line Items]
Percentage of sales commission on gross proceeds for common stock sold through sales agreement	3.00%