Organization and Operations - Liquidity (Details) $ / shares in Units, $ in Thousands		1 Months Ended	9 Months Ended
	Oct. 01, 2017 USD ($) $ / shares shares	Aug. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) $ / shares shares	Oct. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Common stock offering
Accumulated deficit			$ (165,937)			$ (144,070)
Cash and Cash Equivalents, at Carrying Value			$ 21,713			$ 23,596	$ 26,464	$ 62,780
Common Stock | Cowen
Common stock offering
Percentage of commission payable to underwriter based on proceeds from common stock		0.03
Common Stock | First ATM Program
Common stock offering
Number of shares issued | shares			4,054,582
Share price (in dollars per share) | $ / shares			$ 1.77
Additional common stock issued			$ 7,200
Net proceeds			$ 6,900
Common Stock | First ATM Program | Cowen
Common stock offering
Aggregate maximum offering amount		$ 10,000			$ 8,800
Common Stock | Second ATM Program | Subsequent Events | Cowen
Common stock offering
Aggregate maximum offering amount				$ 10,000
Number of shares issued | shares	425,374
Share price (in dollars per share) | $ / shares	$ 2.13
Net proceeds	$ 900