Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues
Total revenues	$ 449.7		$ 1,353.5
Before topic 606
Revenues
Total revenues		$ 381.5		$ 1,092.1
Product revenues, net
Revenues
Total revenues	367.7		1,067.7
Product revenues, net | Before topic 606
Revenues
Total revenues		322.0		878.5
JAKAFI Product Revenues
Revenues
Total revenues	347.6		1,006.9
JAKAFI Product Revenues | Before topic 606
Revenues
Total revenues		303.9		831.0
ICLUSIG Product Revenues
Revenues
Total revenues	20.1		60.8
ICLUSIG Product Revenues | Before topic 606
Revenues
Total revenues		18.1		47.5
Product royalty revenues
Revenues
Total revenues	61.9		165.6
Product royalty revenues | Before topic 606
Revenues
Total revenues		44.5		108.5
JAKAFI Royalty Revenues
Revenues
Total revenues	50.9		139.4
JAKAFI Royalty Revenues | Before topic 606
Revenues
Total revenues		41.3		104.0
OLUMIANT Royalty Revenues
Revenues
Total revenues	11.0		26.2
OLUMIANT Royalty Revenues | Before topic 606
Revenues
Total revenues		3.2		4.5
Milestone revenues
Revenues
Total revenues	20.0		120.0
Milestone revenues | Before topic 606
Revenues
Total revenues		$ 15.0		105.0
Other revenues
Revenues
Total revenues	$ 0.1		$ 0.2
Other revenues | Before topic 606
Revenues
Total revenues				$ 0.1