Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
5.00% Convertible Senior Notes Due 2027
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share	12,321,900
Shares Issuable upon Exercise of Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share	9,863,703	7,919,890
Non-vested Shares under Restricted Stock Grants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share	4,964,544	5,457,806