License, Collaboration and Other Significant Agreements - Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Contract liabilities:
Balance at End of Period	$ 51,694
Other current assets
Contract assets:
Balance at Beginning of Period		$ 0
Additions		10,000
Deductions		(10,000)
Balance at End of Period		0
Accounts receivable
Contract assets:
Balance at Beginning of Period	15,822	1,587
Additions	143,148	134,268
Deductions	(156,209)	(131,651)
Balance at End of Period	2,761	4,204
Prepaid expenses and other current assets
Contract assets:
Balance at Beginning of Period	0
Additions	1,248
Deductions	0
Balance at End of Period	1,248
Deferred revenue
Contract liabilities:
Balance at Beginning of Period	72,950	112,689
Additions	110,295	131,444
Deductions	(131,551)	(168,104)
Balance at End of Period	51,694	76,029
Accounts payable
Contract liabilities:
Balance at Beginning of Period	0	13,492
Additions	10,097	0
Deductions	(5,651)	(13,492)
Balance at End of Period	4,446	$ 0
Accrued expenses and other current liabilities
Contract liabilities:
Balance at Beginning of Period	0
Additions	615
Deductions	(615)
Balance at End of Period	$ 0