Collaboration Agreements - Merck KGaA (Detail) - Merck KGaA $ in Thousands	1 Months Ended	12 Months Ended		36 Months Ended
	Jun. 30, 2014 USD ($) milestone target	Dec. 31, 2020 USD ($) target	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($) target	Dec. 31, 2018 target
Collaboration agreements
Upfront payment received	$ 12,000
Amount of additional fees receivable when target is designated and commercial license to target is granted	$ 0
Number of targets | target	6
Number of targets designated | target		6		6	6
Aggregate milestones	$ 780,000
Development milestones	84,000
Regulatory milestones	264,000
Sales milestones	$ 432,000
Number of individual development milestones per target | milestone	6
Number of individual regulatory milestones per target | milestone	5
Number of individual commercial milestones | milestone	3
Amount of development milestone payment received		$ 0	$ 0	$ 3,000
Next potential development milestone payment eligible to receive		$ 500
Prior written notice for termination period		60 days