Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Number of shares
Outstanding at beginning of period (in shares)	3,134,094
Granted (in shares)	1,091,000
Exercised (shares)	0
Forfeited (in shares)	(29,256)
Expired (in shares)	(188)
Outstanding at end of period (in shares)	4,195,650	3,134,094
Exercisable at end of period (in shares)	1,954,190
Weighted-average exercise price
Outstanding at beginning of period (in dollars per share)	$ 6.23
Granted (in dollars per share)	2.01
Exercised (in dollars per share)	0.00
Forfeited (in dollars per share)	4.61
Expired (in dollars per share)	4.24
Outstanding at end of period (in dollars per share)	5.15	$ 6.23
Exercisable at end of period (in dollars per share)	$ 7.50
Additional disclosures
Weighted-average remaining contractual term (in years), outstanding	8 years	8 years
Weighted-average remaining contractual term (in years), exercisable	6 years 11 months
Aggregate intrinsic value, outstanding	$ 43	$ 1,630
Aggregate intrinsic value, exercisable	$ 0