Collaborative Arrangements - Kymera, Moderna and Other In-License Agreements (Details)	1 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	May 31, 2019 USD ($) target	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Investment in collaborative partner, pursuant to convertible loan agreement			$ 84,600,000	$ 63,300,000	$ 46,900,000
Kymera Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Up-front payment		$ 50,000,000.0		$ 50,000,000.0
Right to license, number of targets (up to) | target		6
Collaborative arrangement development and regulatory potential milestone payments maximum		$ 170,000,000.0
Investment in collaborative partner, pursuant to convertible loan agreement		$ 20,000,000.0
Moderna Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement development and regulatory potential milestone payments maximum	$ 380,000,000.0
Collaborative arrangement, up-front payment paid	$ 75,000,000.0
Skyhawk Therapeutics Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Up-front payment			$ 40,000,000.0