Basis of Presentation and Summary of Significant Accounting Policies - Stock Excluded From Calculation (Details) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	50,626	45,891
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	11,044	12,469
Shares issuable upon conversion of convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	35,582	33,422
Shares issuable under Notes Conversion Agreement
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	4,000	0