Stock-based Compensation - Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Number of Shares Subject to Outstanding Options
Outstanding, beginning of period (shares) | shares	3,918
Granted (shares) | shares	971
Exercised (shares) | shares	(398)
Forfeited (shares) | shares	(601)
Outstanding, end of period (shares) | shares	3,890
Options exercisable (shares) | shares	2,477
Options vested and expected to vest (shares) | shares	3,693
Weighted-average Exercise Price of Outstanding Options
Outstanding, beginning of period (usd per share) | $ / shares	$ 4.49
Granted (usd per share) | $ / shares	4.16
Exercised (usd per share) | $ / shares	2.60
Forfeited/Expired (usd per share) | $ / shares	5.76
Outstanding, end of period (usd per share) | $ / shares	4.40
Options exercisable (usd per share) | $ / shares	4.84
Options vested and expected to vest (usd per share) | $ / shares	$ 4.42
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual terms	6 years 6 months 15 days
Weighted average remaining contractual terms, exercisable options	5 years 3 months 22 days
Weighted average remaining contractual terms, vested and expected to vest options	6 years 4 months 24 days
Aggregate intrinsic value | $	$ 4,494
Aggregate intrinsic value, exercisable options | $	3,138
Aggregate intrinsic value, options vested and expected to vest | $	$ 4,381