Stock-Based Compensation (Details) $ / shares in Units, $ in Thousands	1 Months Ended		5 Months Ended	6 Months Ended	12 Months Ended
	Feb. 29, 2016 shares	Jun. 30, 2015 shares	Apr. 30, 2016 USD ($) shares	Oct. 31, 2016 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares period shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($)
Stock Based Compensation
Proceeds from issuance of common stock under employee stock purchase plan | $					$ 2,589
2015 Plan
Stock Based Compensation
Shares reserved for issuance		3,451,495			13,094,869
Shares reserved for issuance as a proportion common stock outstanding (as a percent)					4.00%
2015 Plan | Minimum
Stock Based Compensation
Shares reserved for issuance					3,500,000
2007 Plan
Stock Based Compensation
Shares reserved for issuance					7,713,510
Employee stock purchase plan
Stock Based Compensation
Shares reserved for issuance		893,548			1,056,344
Shares reserved for issuance as a proportion common stock outstanding (as a percent)					1.00%
Price in relation to fair market value of common stock on the date of grant, lower range limit (as a percent)					85.00%
Maximum offering period, term					27 months
Number of expected offering periods each year | period					2
Offering period, expected term					6 months
Issuance of common stock under employee stock purchase plan (in shares)			116,215	224,637
Proceeds from issuance of common stock under employee stock purchase plan | $			$ 1,000	$ 1,600
Employee stock purchase plan | Minimum
Stock Based Compensation
Shares reserved for issuance					880,000
Employee and non-employee stock options
Stock Based Compensation
Stock based compensation expense | $					$ 10,601	$ 7,326	$ 5,157
Shares available for issuance					4,115,000	3,743,000
Employee and non-employee stock options | 2015 Plan
Stock Based Compensation
Vesting period					4 years
Expiration period		10 years
Employee and non-employee stock options | 2007 Plan
Stock Based Compensation
Vesting period					4 years
Expiration period					10 years
Stock options, exercise price range, number outstanding (in shares)					6,098,564
Stock options, exercise price range, lower range limit (in dollars per share) | $ / shares					$ 0.0978
Stock options, exercise price range, upper range limit (in dollars per share) | $ / shares					12.8501
Stock options, exercise price range, weighted-average exercise price (in dollars per share) | $ / shares					$ 2.71
Shares exercised and unvested						1,300,000
Period after Market Stand-off repurchase right expires						210 days
Accelerated stock-based compensation expense | $						$ 1,300
Stock appreciation rights | 2015 Plan
Stock Based Compensation
Vesting period					4 years
Expiration period					10 years
Restricted shares | Non-employee service provider
Stock Based Compensation
Shares granted	24,540
Restricted stock units
Stock Based Compensation
Shares granted					212,000