Stock Incentive Plans - Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Shares Available for Grant
Balance at the beginning of the period (in shares)	1,058,359
Additional options authorized (in shares)	1,107,411
Granted (in shares)	(1,440,350)
Canceled (in shares)	225,066
Balance at the end of the period (in shares)	950,486	1,058,359
Stock Options Outstanding
Balance at beginning of the period (in shares)	4,179,521
Granted (in shares)	1,440,350
Canceled (in shares)	(218,061)
Exercised (in shares)	(113,923)
Balance at the end of the period (in shares)	5,287,887	4,179,521
Options vested and exercisable at the end of the period (in shares)	2,568,269
Options vested and expected to vest at the end of the period (in shares)	5,059,400
Weighted Average Exercise Price
Balance at beginning of the period (in dollars per share)	$ 8.03
Granted (in dollars per share)	6.15
Canceled (in dollars per share)	10.42
Exercised (in dollars per share)	2.50
Balance at the end of the period (in dollars per share)	7.54	$ 8.03
Options vested and exercisable at the end of the period (in dollars per share)	7.15
Options vested and expected to vest at the end of the period (in dollars per share)	$ 7.54
Weighted Average Remaining Contractual Life
Balance (in years)	7 years 7 months 17 days	7 years 6 months
Options vested and exercisable at the end of the period (in years)	6 years 4 months 2 days
Options vested and expected to vest at the end of the period (in years)	7 years 6 months 22 days
Aggregate Intrinsic Value
Balance at the beginning of the period (in dollars)	$ 6,511
Balance at the end of the period (in dollars)	8,640	$ 6,511
Options vested and exercisable at the end of the period (in dollars)	6,206
Options vested and expected to vest at the end of the period (in dollars)	$ 8,421