Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Number of Shares
Beginning balance - Outstanding (shares)	1,819,444
Granted (shares)	982,803
Exercised (shares)	0
Canceled (shares)	(73)
Ending balance - Outstanding (shares)	2,802,174	1,819,444
Exercisable (shares)	1,331,565
Vested or expected to vest (shares)	2,802,174
Weighted- Average Exercise Price
Beginning balance - Outstanding (in dollars per share)	$ 7.52
Granted (in dollars per share)	3.07
Exercised (in dollars per share)	0.00
Canceled (in dollars per share)	9.64
Ending balance - Outstanding (in dollars per share)	5.96	$ 7.52
Exercisable (in dollars per share)	7.72
Vested or expected to vest (in dollars per share)	$ 5.96
Weighted- Average Remaining Contractual Life (in years)
Balance - Outstanding	7 years 1 month 24 days	6 years 11 months 23 days
Exercisable	5 years 8 months 27 days
Vested and expected to vest	7 years 1 month 24 days
Aggregate Intrinsic Value ($000)
Balance - Outstanding	$ 2	$ 32
Exercisable	0
Vested and expected to vest	$ 2