Stockholders' Equity - Common Stock and Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended		3 Months Ended	6 Months Ended
	Apr. 12, 2017	Apr. 03, 2017	Dec. 22, 2016	Apr. 30, 2017	Jan. 31, 2014	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Stockholders' equity
Proceeds from exercise of warrants							$ 17,702	$ 111
Increase in additional paid-in capital				$ 27,100
Reduction of warrant liability				$ 27,100
Common Stock, par value (in dollars per share)						$ 0.01	$ 0.01		$ 0.01
Net proceeds							$ 20,684
At Market Issuance Sales Agreement
Stockholders' equity
Authorized amount		$ 75,000
Shares of common stock issuances		9,314,666
Net proceeds		$ 20,700
Warrants issued in December 2016
Stockholders' equity
Class of Warrant or Right Issued			10,501,500
Exercise price of warrants (in dollars per share)	$ 1.50		$ 1.50
Number of warrants exercised (in shares)	10,501,500
Proceeds from exercise of warrants	$ 15,100
Shares of common stock that can be purchased from warrants issued	5,250,750
Per share price of shares of common stock	$ 2.69
Warrants issued in January, 2014
Stockholders' equity
Class of Warrant or Right Issued					4,000,000
Exercise price of warrants (in dollars per share)				$ 0.65	$ 4.00				$ 0.65
Number of warrants exercised (in shares)				4,000,000		4,000,000
Proceeds from exercise of warrants				$ 2,600