Revenue from Contracts with Customers - Summary of Collaboration and License Agreement Revenues by Collaborator (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Collaboration and license agreement revenues	$ 169,424	$ 135,291	$ 480,187	$ 352,645
License and Service [Member]
Disaggregation of Revenue [Line Items]
Collaboration and license agreement revenues	19,786	$ 39,444	76,524	$ 82,779
License and Service [Member] | Takeda Collaboration and License Agreement [Member]
Disaggregation of Revenue [Line Items]
Collaboration and license agreement revenues	18,805		41,122
License and Service [Member] | AbbVie Collaboration and License Agreement [Member]
Disaggregation of Revenue [Line Items]
Collaboration and license agreement revenues	300		13,000
License and Service [Member] | Genmab Collaboration and License Agreement [Member]
Disaggregation of Revenue [Line Items]
Collaboration and license agreement revenues	0		7,000
License and Service [Member] | GSK Collaboration and License Agreement [Member]
Disaggregation of Revenue [Line Items]
Collaboration and license agreement revenues	0		6,000
License and Service [Member] | Other Collaboration and License Agreement [Member]
Disaggregation of Revenue [Line Items]
Collaboration and license agreement revenues	$ 681		$ 9,402