Net Loss per Share Attributable to Common Stockholders - Anti-dilutive Securities (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the computation of diluted net loss per share (in shares)	1,084	0	2,906	0
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the computation of diluted net loss per share (in shares)	1,054	0	2,646	0
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the computation of diluted net loss per share (in shares)	30	0	260	0