Business Overview and Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of business segments | segment	1
Retained Earnings (Accumulated Deficit)	$ 10,893,000,000.0	$ 7,379,800,000
Allowance for doubtful accounts receivable, current	0	0
Provision for doubtful accounts	0	0
Up-front and development milestone revenue recognized	$ 276,700,000	$ 207,200,000
Three individual customers | Customer concentration risk | Gross Sales Revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk, percentage	93.00%	97.00%
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset			$ 33,200,000
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained Earnings (Accumulated Deficit)				$ (143,400,000)
Deferred revenue				$ 143,400,000