Stock Incentive Plans - Stock Option Plan Activity (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Stock options
Outstanding at beginning of year (in shares)			2,845,626
Granted (in shares)			2,133,845
Exercised (in shares)			(2,917)
Cancelled or forfeited (in shares)			(487,097)
Outstanding at end of year (in shares)	4,489,457		4,489,457		2,845,626
Vested and Exercisable to vest at end of year (in shares)	1,734,044		1,734,044
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)			$ 4.53
Granted (in dollars per share)			0.98
Exercised (in dollars per share)			1.24
Cancelled or forfeited (in dollars per share)			2.93
Outstanding at end of year (in dollars per share)	$ 3.02		3.02		$ 4.53
Vested and Exercisable at end of year (in dollars per share)	$ 5.24		$ 5.24
Weighted Average Remaining Contractual Term (years)
Outstanding at end of year			8 years 2 months 9 days		7 years 9 months
Vested and Exercisable at end of year			6 years 6 months 15 days
Aggregate Intrinsic Value
Outstanding at the beginning of the year			$ 216,000
Outstanding at the end of the year	$ 102,000		102,000		$ 216,000
Stock options
Unrecognized stock-based compensation expense
Intrinsic value of options exercised	0	$ 0	1,000	$ 41,000
Adjusted fair value of options vested	$ 300,000	$ 600,000	$ 1,400,000	$ 1,800,000
Weighted average grant date fair value of options granted (in dollars per share)	$ 0.46	$ 0.86	$ 0.66	$ 0.85
Unrecognized compensation expense related to unvested stock option awards	$ 2,700,000		$ 2,700,000
Weighted-average amortization period over which cost is expected to be recognized			1 year 9 months 18 days