Stock Incentive Plans - Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Stock options
Outstanding at beginning of year (in shares)			2,270,169
Granted (in shares)			876,740
Exercised (in shares)			(22,879)
Cancelled or forfeited (in shares)			(284,623)
Outstanding at end of year (in shares)	2,839,407		2,839,407		2,270,169
Vested and Exercisable to vest at end of year (in shares)	1,172,834		1,172,834
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)			$ 6.11
Granted (in dollars per share)			1.24
Exercised (in dollars per share)			1.01
Cancelled or forfeited (in dollars per share)			7.27
Outstanding at end of year (in dollars per share)	$ 4.54		4.54		$ 6.11
Vested and Exercisable at end of year (in dollars per share)	$ 5.82		$ 5.82
Weighted Average Remaining Contractual Term (years)
Outstanding at end of year			7 years 11 months 27 days		8 years 1 month 21 days
Vested and Exercisable at end of year			6 years 8 months 1 day
Aggregate Intrinsic Value
Outstanding at the beginning of the year			$ 613
Outstanding at the end of the year	$ 817		817		$ 613
Aggregate intrinsic value of options vested and exercisable	53		53
Stock options
Unrecognized stock-based compensation expense
Intrinsic value of options exercised	0	$ 30	41	$ 200
Fair value of options vested	$ 600	$ 800	$ 1,800	$ 1,900
Weighted average grant date fair value of options granted (in dollars per share)	$ 0.86	$ 2.84	$ 0.85	$ 2.88
Unrecognized compensation expense related to unvested stock option awards	$ 3,700		$ 3,700
Weighted-average amortization period over which cost is expected to be recognized			2 years 1 month 6 days