Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 39.3	$ (7.7)
Other comprehensive income (loss), net of tax:
Change in foreign currency translation adjustments	(3.0)	1.1
Change in net unrealized gains (losses), on short-term investments	(1.8)	1.9
Total other comprehensive income (loss), net of tax	(4.8)	3.0
Comprehensive income (loss)	$ 34.5	$ (4.7)