Summary of significant accounting policies - Narrative 1 (Details) $ in Thousands		3 Months Ended
	Jan. 01, 2018 USD ($)	Mar. 31, 2018 USD ($) item issuer instrument	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
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
Accumulated Other Comprehensive Income (Loss)
Net income		$ (41,140)	$ (187,083)
ASU 2016-01 | Calithera
Accumulated Other Comprehensive Income (Loss)
Net income	$ 2,800
JAKAFI
Inventory
Shelf life for finished goods inventory, maximum		36 months
ICLUSIG
Inventory
Shelf life for finished goods inventory, maximum		24 months