License Agreement (Details) - USD ($)		3 Months Ended
	Feb. 05, 2019	Mar. 31, 2019	Mar. 31, 2018
License Agreement [Line Items]
Customary supply agreement, initial term (in years)	2 years
Customary supply agreement, automatic renewal term (in years)	2 years
Term from Completion Date (in years)	10 years
Renewal term (in years)	5 years
Written notice period (in months)	18 months
Termination from breach uncured (in days)	90 days
Termination from breach uncured, non-payment (in days)	15 days
Deferred revenue		$ 24,167,000	$ 0
Aegerion
License Agreement [Line Items]
One-time upfront payment	$ 25,000,000.0
One-time payment due within 45 days	$ 5,000,000.0
Number of days following the Completion Date	45 days
Percentage of net sales	22.50%
Percentage of all other sublicense revenues	20.00%
Commercial milestone payments receivable (up to)	$ 80,000,000.0
First installment payable	12,500,000
Cumulative net sales, first threshold	70,000,000.0
Cumulative net sales, second threshold	280,000,000.0
Cumulative net sales, second threshold, incremental installments	5,000,000.0
Cumulative net sales, maximum	$ 700,000,000.0
Percentage of upfront payment due to UPenn	15.00%
Percentage of net sales retained	40.00%
Percentage of net sales remitted	60.00%
Transitional services at hourly rate, term (in years)	6 months
Proceeds from upfront payment	$ 15,000,000.0
JUXTAPID
License Agreement [Line Items]
Consideration for license performance obligation		30,000,000.0
Proceeds from upfront payment		25,000,000.0
Deferred revenue		$ 800,000
JUXTAPID | Aegerion
License Agreement [Line Items]
Percentage of net sales remitted	60.00%
JUXTAPID | UPenn
License Agreement [Line Items]
Percentage of milestone payment due to UPenn	15.00%
Percentage of royalty payments received	25.00%