Agreements - Bayer (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2008
Collaborative Agreements disclosures
Total revenues	$ 44,864	$ 13,281	$ 15,542	$ 8,584	$ 13,416	$ 10,928	$ 9,287	$ 19,815	$ 39,448	$ 8,480	$ 39,020	$ 28,499	$ 82,271	$ 53,446	$ 115,447
Bayer | Minimum
Collaborative Agreements disclosures
Percentage of royalty payments																4.00%
Bayer | Maximum
Collaborative Agreements disclosures
Percentage of royalty payments																7.00%
Bayer | Development milestones
Collaborative Agreements disclosures
Potential milestone payment	2,000												2,000			$ 16,000
Bayer | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment	6,000												6,000			44,500
Bayer | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment																110,000
Upfront payment | Bayer
Collaborative Agreements disclosures
Total revenues																4,000
License and milestone fees
Collaborative Agreements disclosures
Total revenues	$ 29,551	$ 79	$ 5,079	$ 79	$ 1,747	$ 672	$ 1,321	$ 11,540	$ 29,580	$ 79	$ 31,080	$ 18,730	34,788	$ 15,280	$ 79,469
License and milestone fees | Bayer
Collaborative Agreements disclosures
Total revenues													$ 13,000
Potential milestone payment																$ 170,500