Agreements - Bayer (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	108 Months Ended
	Jan. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2008	Dec. 31, 2016
Collaborative Agreements disclosures
Amount of arrangement consideration included in license and milestone fees		$ 79	$ 76	$ 49,889	$ 10,229
Bayer
Collaborative Agreements disclosures
Payments received under collaboration agreement				13,000		$ 4,000	$ 13,000
Potential milestone payments						$ 170,500
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 payments		$ 2,000		$ 2,000		$ 16,000
Bayer | Phase 2 clinical trial
Collaborative Agreements disclosures
Payments received under collaboration agreement	$ 10,000
Bayer | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payments						44,500
Bayer | Sales milestones
Collaborative Agreements disclosures
Potential milestone payments						$ 110,000