Revenue from Collaboration and License Agreements - Summary of Net Revenue from Partners in Connection with Collaboration and License Agreements (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	$ 22,377		$ 26,623	$ 38,451	$ 190,439
Collaboration and License Agreement with PTC Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue		$ 4,000	6,000
Licensing Revenue and Research and Development and License Revenue Under Collaborative Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	6,013		16,758	6,928	173,820
Licensing Revenue and Research and Development and License Revenue Under Collaborative Agreement [Member] | License Agreement with Pfizer [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	5,735			6,339
Licensing Revenue and Research and Development and License Revenue Under Collaborative Agreement [Member] | Strategic Collaboration with Novartis [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	$ 278		10,722	$ 589	167,784
Licensing Revenue and Research and Development and License Revenue Under Collaborative Agreement [Member] | Collaboration and License Agreement with PTC Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue			$ 6,036		$ 6,036