Concentration of credit risk (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Milestone Revenues | Customer Concentration Risk | Collaboration Partner C
Concentration of risk
Percentage of concentration risk	100.00%
Net Product Revenues | Customer Concentration Risk | Customer A
Concentration of risk
Percentage of concentration risk	18.00%	22.00%
Net Product Revenues | Customer Concentration Risk | Customer B
Concentration of risk
Percentage of concentration risk	15.00%	13.00%
Net Product Revenues | Customer Concentration Risk | Customer C
Concentration of risk
Percentage of concentration risk	16.00%	14.00%
Net Product Revenues | Customer Concentration Risk | Customer D
Concentration of risk
Percentage of concentration risk	12.00%	11.00%
Accounts Receivable | Credit Concentration Risk | Collaboration Partner A, B and C
Concentration of risk
Percentage of concentration risk	26.00%		42.00%
Accounts Receivable | Credit Concentration Risk | Customer A, B, C and D
Concentration of risk
Percentage of concentration risk	37.00%		30.00%