Stockholders' Equity - 2017 Public Offering of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Aug. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Sale of stock
Proceeds from the issuance of common stock, net		$ 18,536	$ 37,527
2017 Public Offering
Sale of stock
Proceeds from the issuance of common stock, net	$ 18,500
Common Stock | 2017 Public Offering
Sale of stock
Common stock issued (in shares)	5,333,334
Share price (in dollars per share)	$ 3.75