Stock Incentive Plans - Activity Under Stock Option Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 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)	1,114,416
Canceled (in shares)	358,199
Balance at the end of the period (in shares)	887,724	1,058,359
Stock Options Outstanding
Balance at beginning of the period (in shares)	4,179,521
Canceled (in shares)	(358,199)
Exercised (in shares)	(212,740)
Balance at the end of the period (in shares)	5,251,832	4,179,521
Options vested and exercisable at the end of the period (in shares)	2,628,328
Options vested and expected to vest at the end of the period (in shares)	4,962,370
Weighted Average Exercise Price
Balance at beginning of the period (in dollars per share)	$ 8.03
Canceled (in dollars per share)	10.29
Exercised (in dollars per share)	2.53
Balance at the end of the period (in dollars per share)	7.56	$ 8.03
Options vested and exercisable at the end of the period (in dollars per share)	7.42
Options vested and expected to vest at the end of the period (in dollars per share)	$ 7.58
Weighted Average Remaining Contractual Life
Balance	7 years 2 months 26 days	7 years 6 months
Options vested and exercisable at the end of the period	5 years 10 months 20 days
Options vested and expected to vest at the end of the period	7 years 1 month 27 days
Aggregate Intrinsic Value
Balance at the beginning of the period (in dollars)	$ 6,511
Balance at the end of the period (in dollars)	8,515	$ 6,511
Options vested and exercisable at the end of the period (in dollars)	6,008
Options vested and expected to vest at the end of the period (in dollars)	$ 8,254
Employee stock options
Shares Available for Grant
Granted (in shares)	(1,618,250)
Stock Options Outstanding
Granted (in shares)	1,618,250
Weighted Average Exercise Price
Granted (in dollars per share)	$ 6.30
Restricted stock units (RSUs)
Shares Available for Grant
Granted (in shares)	(25,000)
Stock Options Outstanding
Granted (in shares)	25,000

Number of additional shares authorized for issuance under an established share-based compensation plan.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.