Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Total revenues	$ 521.5		$ 903.8
Before topic 606
Revenues
Total revenues		$ 326.5		$ 710.6
Product revenues, net
Revenues
Total revenues	365.5		700.0
Product revenues, net | Before topic 606
Revenues
Total revenues		291.7		556.5
JAKAFI Product Revenues
Revenues
Total revenues	345.6		659.3
JAKAFI Product Revenues | Before topic 606
Revenues
Total revenues		276.0		527.1
ICLUSIG Product Revenues
Revenues
Total revenues	19.9		40.7
ICLUSIG Product Revenues | Before topic 606
Revenues
Total revenues		15.7		29.4
Product royalty revenues
Revenues
Total revenues	56.0		103.7
Product royalty revenues | Before topic 606
Revenues
Total revenues		34.8		64.0
JAKAFI Royalty Revenues
Revenues
Total revenues	47.1		88.4
JAKAFI Royalty Revenues | Before topic 606
Revenues
Total revenues		33.9		62.7
OLUMIANT Royalty Revenues
Revenues
Total revenues	8.9		15.3
OLUMIANT Royalty Revenues | Before topic 606
Revenues
Total revenues		$ 0.9		1.3
Milestone revenues
Revenues
Total revenues	$ 100.0		100.0
Milestone revenues | Before topic 606
Revenues
Total revenues				90.0
Other revenues
Revenues
Total revenues			$ 0.1
Other revenues | Before topic 606
Revenues
Total revenues				$ 0.1