Organization and Operations - Liquidity (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended
	Mar. 16, 2017 USD ($)	Aug. 31, 2016 USD ($)	Mar. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)
Common stock offering
Accumulated deficit			$ (151,946)	$ (144,070)
Common Stock
Common stock offering
Percentage of commission payable to underwriter based on proceeds from common stock		0.03
Common Stock | ATM
Common stock offering
Number of shares issued | shares			1,168,419
Share price (in dollars per share) | $ / shares			$ 1.95
Additional common stock issued	$ 3,900		$ 2,300
Net proceeds			2,200
Aggregate maximum offering amount	$ 4,900
Remaining common stock available for sale under offering program			4,900
Common Stock | ATM | Cowen
Common stock offering
Aggregate maximum offering amount		$ 10,000
Remaining common stock available for sale under offering program			$ 4,100