Common Stock and Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Number of options
Beginning number of options (in shares), outstanding | shares	5,126,000
Number of options, Granted (in shares) | shares	4,966,000
Number of options, Exercised (in shares) | shares	(90,000)
Number of options, Canceled/forfeited/expired (in shares) | shares	(1,071,000)
End number of options (in shares), outstanding | shares	8,931,498
Number of options, Vested or expected to vest (in shares) | shares	8,278,000
Number of options, Exercisable (in shares) | shares	2,882,000
Weighted average exercise price
Beginning, Weighted average exercise price, Options outstanding (in dollars per share) | $ / shares	$ 8.91
Weighted average exercise price, Granted (in dollars per share) | $ / shares	4.93
Weighted average exercise price, Exercised (in dollars per share) | $ / shares	3.45
Weighted average exercise price, Canceled/forfeited/expired (in dollars per share) | $ / shares	9.32
Ending, Weighted average exercise price, Options outstanding (in dollars per share) | $ / shares	6.70
Weighted average exercise price, Vested or expected to vest (in dollars per share) | $ / shares	6.82
Weighted average exercise price, Exercisable (in dollars per share) | $ / shares	$ 7.58
Weighted average remaining contractual term
Weighted average remaining contractual term, Options outstanding	8 years 1 month 21 days
Weighted average remaining contractual term, Vested or expected to vest	8 years 15 days
Weighted average remaining contractual term, Exercisable	5 years 11 months 27 days
Aggregate intrinsic value
Aggregate intrinsic value, Options outstanding | $	$ 34,680
Aggregate intrinsic value, Vested or expected to vest | $	31,463
Aggregate intrinsic value, Exercisable | $	$ 9,688