Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 493.6	$ 101.1	$ (127.1)
Other comprehensive income, net of tax:
Foreign currency translation gain	1.1	0.4	4.0
Unrealized gain (loss) on marketable debt securities	(0.2)	0.4	0.1
Total other comprehensive income, net of tax	0.9	0.8	4.1
Comprehensive income (loss)	$ 494.5	$ 101.9	$ (123.0)