Annual report pursuant to Section 13 and 15(d)

Common Stock and Net Loss per Common Share - Schedule of potential common shares that were excluded from the computation of diluted net loss per share (Details)

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Common Stock and Net Loss per Common Share - Schedule of potential common shares that were excluded from the computation of diluted net loss per share (Details) - shares
shares in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total common stock equivalents (in shares) 72,651 34,786 31,160
Shares issuable upon conversion of preferred stock      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total common stock equivalents (in shares) 46,747 0 0
Restricted stock units      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total common stock equivalents (in shares) 19,276 22,404 17,272
Options to purchase common stock      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total common stock equivalents (in shares) 4,322 9,436 12,816
Performance stock units      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total common stock equivalents (in shares) 1,486 2,369 776
Shares issuable pursuant to the ESPP      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total common stock equivalents (in shares) 820 577 296