Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Partners Capital [Abstract]
Net income (loss)	$ (23.0)	$ (103.9)
Other comprehensive income (loss):
Change in foreign currency translation adjustment	(15.5)	(29.0)
Net change in unrealized gains (losses) on available-for-sale marketable debt securities, net of tax	(0.1)	(1.0)
Other comprehensive income (loss), net of tax	(15.6)	(30.0)
Comprehensive income (loss)	$ (38.6)	$ (133.9)