Summary of significant accounting policies - Narrative 1 (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($) item	Sep. 30, 2017 USD ($) item issuer instrument	Dec. 31, 2016 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	$ 0
Variable Interest Entities
Number of entities in which variable interest held | item	0	0
Impairment of Long-Lived Assets
Write-off of the acquired IPR&D		$ 12,000
IPR&D
Impairment of Long-Lived Assets
Write-off of the acquired IPR&D	$ 12,000	$ 12,000
JAKAFI
Inventory
Shelf life for finished goods inventory, maximum		36 months
ICLUSIG
Inventory
Shelf life for finished goods inventory, maximum		24 months