Net income (loss) per share - Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss per Share Attributable to Common Stockholders (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	5,747	508	5,747	526
Employee Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	3,898	474	3,898	492
Restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	1,663	34	1,663	34
Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	186		186