Concentration of credit risk (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Milestone Revenues | Customer Concentration Risk | Collaboration Partner A
Concentration of risk
Percentage of concentration risk				24.00%
Milestone Revenues | Customer Concentration Risk | Collaboration Partner B
Concentration of risk
Percentage of concentration risk	100.00%	100.00%	100.00%	76.00%
Net Product Revenues | Customer Concentration Risk | Customer A
Concentration of risk
Percentage of concentration risk	19.00%	24.00%	20.00%	25.00%
Net Product Revenues | Customer Concentration Risk | Customer B
Concentration of risk
Percentage of concentration risk	12.00%	16.00%	13.00%	16.00%
Net Product Revenues | Customer Concentration Risk | Customer C
Concentration of risk
Percentage of concentration risk	16.00%	14.00%	15.00%	13.00%
Net Product Revenues | Customer Concentration Risk | Customer D
Concentration of risk
Percentage of concentration risk	12.00%	8.00%	11.00%	8.00%
Accounts Receivable | Credit Concentration Risk | Collaboration Partner A and B
Concentration of risk
Percentage of concentration risk			33.00%		47.00%
Accounts Receivable | Credit Concentration Risk | Customer A, B, C and D
Concentration of risk
Percentage of concentration risk			31.00%		25.00%