Stock‑Based Compensation (Options) (Details) - Employee and non-employee stock options - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Stock Based Compensation
Shares available for grant, beginning balance	294
Additional shares authorized	1,534
Options granted (in shares)	(1,465)
Options forfeited (in shares)	346
Shares available for grant, end balance	709	294
Number of shares
Outstanding, beginning balance (in shares)	8,463
Options granted (in shares)	1,465
Options exercised (in shares)	(179)
Options forfeited (in shares)	(346)
Outstanding, end balance (in shares)	9,403	8,463
Exercisable (in shares)	5,390
Vested and expected to vest (in shares)	8,443
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per shares)	$ 2.28
Granted (in dollars per share)	8.96
Exercised (in dollars per share)	1.71
Forfeited (in dollars per share)	3.26
Outstanding, end balance (in dollars per shares)	3.30	$ 2.28
Exercisable (in dollars per share)	1.65
Vested and expected to vest (in dollars per share)	$ 3.08
Additional disclosures
Weighted average contractual term, options outstanding	8 years 7 months 28 days	8 years 9 months 29 days
Exercisable (in years)	5 years 8 months 19 days
Vested and expected to vest (in years)	8 years 3 months 26 days
Aggregate intrinsic value, options outstanding	$ 137,066
Aggregate intrinsic value, options exercisable	87,708
Aggregate intrinsic value, vested and expected to vest	$ 124,597