Net Loss Per Share Attributable to Common Stockholders - Anti-dilutive Shares (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	466,704	444,417
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	308,373	308,373
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	76,584	77,341
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	81,498	58,447
Redeemable convertible preferred stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	249	89
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	0	167