License, Collaboration and Other Significant Agreements - Schedule of Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Contract liabilities:
Balance at End of Period	$ 58,071
Other current assets
Contract assets:
Balance at Beginning of Period		$ 0
Additions		10,000
Deductions		0
Balance at End of Period		10,000
Accounts receivable
Contract assets:
Balance at Beginning of Period	15,822	1,587
Additions	118,368	81,830
Deductions	(115,382)	(75,260)
Balance at End of Period	18,808	8,157
Prepaid expenses and other current assets
Contract assets:
Balance at Beginning of Period	0
Additions	756
Deductions	0
Balance at End of Period	756
Deferred revenue
Contract liabilities:
Balance at Beginning of Period	72,950	112,689
Additions	90,471	91,351
Deductions	(105,350)	(108,166)
Balance at End of Period	58,071	95,874
Accounts payable
Contract liabilities:
Balance at Beginning of Period	0	13,492
Additions	5,651	0
Deductions	0	(13,492)
Balance at End of Period	5,651	$ 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