Subsequent Events Subsequent events (Details) - USD ($) $ in Millions	1 Months Ended
	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Prepaid research and development		$ 1,690.6	$ 431.6
Skyhawk Therapeutics | Subsequent Event
Subsequent Event [Line Items]
Upfront And Milestone Payments Made To Collaborative Partner	$ 74.0
Additional milestone payment	2,000.0
Prepaid research and development	$ 35.0