Business and Organization - (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	May 24, 2018 $ / shares	Mar. 10, 2017 $ / shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Jul. 02, 2018 $ / shares	Dec. 31, 2016 USD ($)
Subsequent Event [Line Items]
Net loss			$ 10,277	$ 16,240
Accumulated deficit			189,080	178,803
Accumulated deficit			(9,557)	(9,007)		$ (7,861)
Net cash used in operating activities			12,717	17,037
Cash and cash equivalents			14,430	$ 17,417		17,515
Working capital			$ 12,400
Reverse stock split (percentage)	0.2	0.3333
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Accumulated deficit
Subsequent Event [Line Items]
Net loss			$ 10,277	$ 16,240
Accumulated deficit			$ 189,080	$ 178,803		$ 162,563