Agreements - Sanofi (Details) $ in Thousands	1 Months Ended	3 Months Ended												12 Months Ended
	May 31, 2017 item	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Agreements disclosures
Revenue from contract with customer		$ 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
Sanofi
Collaborative Agreements disclosures
Number of compounds | item	4
Sanofi | Development milestones
Collaborative Agreements disclosures
Revenue from contract with customer														26,500
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer		$ 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 | Sanofi
Collaborative Agreements disclosures
Revenue from contract with customer																30,000
License and milestone fees | Sanofi | Development milestones
Collaborative Agreements disclosures
Revenue from contract with customer																6,000
License amendments | Sanofi
Collaborative Agreements disclosures
Revenue from contract with customer																$ 30,000