Summary of significant accounting policies - Narrative 1 (Details) $ in Thousands	1 Months Ended	9 Months Ended
	Apr. 30, 2016 ft²	Sep. 30, 2016 USD ($) item issuer instrument	Dec. 31, 2015 USD ($)
Concentrations of Credit Risk
Number of issuer to which company limits the amount of credit exposure other than US Government guaranteed securities | issuer		1
Number of financial investment to which company limits the amount of credit exposure other than US Government guaranteed securities | instrument		1
Accounts Receivable
Allowance for doubtful accounts | $		$ 0	$ 0
Variable Interest Entities
Number of entities in which variable interest held | item		0
Wilmington, Delaware
Lease Accounting
Square footage of laboratory and office purchased | ft²	190,000
JAKAFI
Inventory
Shelf life for finished goods inventory, maximum		36 months
JAKAFI | Minimum
Inventory
Period of lower average per unit cost of materials		3 months
JAKAFI | Maximum
Inventory
Period of lower average per unit cost of materials		6 months
ICLUSIG
Inventory
Shelf life for finished goods inventory, maximum		24 months