Accounting Policies - Instruments Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	20,007,851	31,112,196	10,568,099
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	13,975,671	10,955,508	8,919,113
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	2,032,180	1,656,688	1,648,986
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	4,000,000	18,500,000	0