Liquidity and Going Concern - Narrative (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	May 19, 2015
Liquidity and Going Concern
Accumulated deficit	$ 226,905,000	$ 223,063,000
Cash	3,341,000	$ 7,839,000	$ 2,698,000	$ 2,958,000
Shelf Registration
Liquidity and Going Concern
Aggregate securities authorized					$ 50,000,000.0
Aggregate securities sold	$ 3,100,000