Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 101.1	$ (127.1)	$ (50.2)
Other comprehensive income (loss), net of income taxes:
Foreign currency translation gain (loss)	0.4	4.0	(1.4)
Unrealized gain (loss) on marketable debt securities	0.4	0.1	(0.2)
Total other comprehensive income (loss), net	0.8	4.1	(1.6)
Comprehensive income (loss)	$ 101.9	$ (123.0)	$ (51.8)