Collaboration and License Agreements (Details) $ in Thousands, € in Millions	1 Months Ended						3 Months Ended				9 Months Ended		12 Months Ended
	Feb. 28, 2019 USD ($)	Nov. 30, 2017 USD ($)	Oct. 31, 2017 USD ($)	Mar. 31, 2015 USD ($)	Oct. 31, 2014 USD ($)	Oct. 31, 2014 EUR (€)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Collaboration and License Agreements [Abstract]
Sanofi termination cash payment							$ 208,000				$ 26,000	$ 208,000
Sanofi Revenue Recognized											286,000	286,000
Ipsen Total Payments							47,200				47,200
Ipsen Maximum Regulatory And Commercial Milestones											9,600
Ipsen Maximum Sales Milestones | €						€ 72
Ipsen Total Upfront Payments				$ 24,500
Ipsen Milestone Payment										$ 6,400
Ipsen Milestone Payment Received	$ 2,300	$ 3,800	$ 3,800					$ 1,300	$ 5,100
Ipsen Revenue Allocated to License Deliverable													$ 1,400	$ 21,200
Ipsen Revenue Allocated to Development Deliverable					$ 1,700
Ipsen Revenue Allocated to Committee Deliverable					$ 100
Ipsen Revenue Recognized											300	$ 3,500
lxrx_sanofi initial cash payment							$ 26,000				26,000
Ipsen Royalty Income_LXRX											$ 300