Stock Incentive Plans - Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Stock options
Outstanding at beginning of period (in shares)			1,723,554
Granted (in shares)			541,395
Exercised (in shares)			(36,880)
Cancelled or forfeited (in shares)			(140,627)
Outstanding at end of period (in shares)	2,087,442		2,087,442		1,723,554
Exercisable at end of period (in shares)	962,927		962,927
Vested or expected to vest at end of period (in shares)	2,013,028		2,013,028
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)			$ 6.66
Granted (in dollars per share)			4.58
Exercised (in dollars per share)			1.86
Cancelled or forfeited (in dollars per share)			6.00
Outstanding at end of period (in dollars per share)	$ 6.25		6.25		$ 6.66
Exercisable at end of period (in dollars per share)	4.46		4.46
Vested or expected to vest at end of period (in dollars per share)	$ 6.20		$ 6.20
Weighted-Average Remaining Contractual Term
Outstanding at beginning of period			7 years 11 months 9 days		7 years 11 months 1 day
Outstanding at end of period			7 years 11 months 9 days		7 years 11 months 1 day
Exercisable at end of period			6 years 8 months 1 day
Vested or expected to vest at end of period			7 years 10 months 21 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period			$ 4,267
Outstanding at the end of the period	$ 986		986		$ 4,267
Exercisable at the end of the period	$ 942		942
Unrecognized stock-based compensation expense
Fair value of options vested			$ 985
Weighted average grant date fair value of options granted (in dollars per share)	$ 3.09	$ 7.71	$ 2.96	$ 7.01
Options to purchase Common stock
Unrecognized stock-based compensation expense
Intrinsic value of options exercised	$ 32,000	$ 0	$ 200	$ 200
Fair value of options vested	600	$ 200	1,100	$ 800
Unrecognized compensation expense related to unvested stock option awards	$ 4,700		$ 4,700
Weighted-average amortization period over which cost is expected to be recognized			2 years 8 months 12 days