Stockholders' Equity - Private Placement and Common Stock Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	9 Months Ended
	Aug. 22, 2018	Feb. 01, 2018	Nov. 02, 2017	Sep. 30, 2018	Sep. 30, 2017	Oct. 05, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Proceeds from common stock offering				$ 22,001	$ 20,302
Issuance of common stock in private placement, net				$ 20,070
Issuance of common stock to consultants, net (in shares)		145,466
Private Placement
Class of Stock [Line Items]
Number of shares issued in transaction (in shares)	4,889,217		10,504,196
Price per share (in dollars per share)	$ 4.50		$ 3.00
Proceeds from common stock offering	$ 22,001
Payments of stock issuance costs	1,931		$ 3,966
Consideration received on transaction	$ 20,070		$ 31,513
Issuance of common stock in private placement, net (in shares)	4,889,217
Cash placement fees	$ 1,680
Expenses reimbursed to placement agents	$ 87
Number of shares called by warrants (in shares)				413,320			413,320
Exercise price (in dollars per share)							$ 3.00
Subsequent Event | Common Stock
Class of Stock [Line Items]
Shares registered for resale (in shares)						5,034,683