Summary of Significant Accounting Policies (Details) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($) Segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reporting segments | Segment		1
Accrued capital expenditures		$ 8,800		$ 11,100
Right-of-use asset acquired in exchange for lease liability		7,000	$ 39,200
Accrued interest receivable	$ 1,900	1,900
Amortization of intangible assets	5,800	10,541	$ 11
Intangible asset, carrying value	305,700	305,700		5,700
Intangible asset, accumulated amortization	16,200	16,200		$ 5,600
Estimated future amortization expense, remainder of fiscal year	5,800	5,800
Estimated future amortization expense, 2021	23,100	23,100
Estimated future amortization expense, 2022	23,100	23,100
Estimated future amortization expense, 2023	23,100	23,100
Estimated future amortization expense, 2024	23,100	23,100
Estimated future amortization expense, 2025	23,100	23,100
Purchase Agreement [Member] | Collaboration and License Agreement Revenues [Member]
Summary Of Significant Accounting Policies [Line Items]
Variable consideration	$ 250,100	$ 250,100
Weighted Average [Member]
Summary Of Significant Accounting Policies [Line Items]
Intangible asset useful life		13 years
Long Term Incentive Plans [Member]
Summary Of Significant Accounting Policies [Line Items]
LTIP estimated unrecognized compensation expense		$ 58,000