Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 585.3	$ 59.0	$ 603.6	$ 75.9
Other comprehensive loss before reclassifications	(2.9)		(5.2)
Amounts reclassified to net loss	0.4		0.4
Other comprehensive income (loss)	(2.5)	0.2	(4.8)	(2.4)
Ending balance	459.1	563.3	459.1	563.3
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	3.1	(5.0)	5.2	(1.6)
Other comprehensive loss before reclassifications	(1.8)		(3.9)
Amounts reclassified to net loss	0.0		0.0
Other comprehensive income (loss)		0.6		(2.8)
Ending balance	1.3	(4.4)	1.3	(4.4)
Unrealized Gain on Available-for-sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.1	1.2	0.3	0.4
Other comprehensive loss before reclassifications	(0.1)		(0.3)
Amounts reclassified to net loss	0.0		0.0
Other comprehensive income (loss)		(0.4)		0.4
Ending balance	0.0	0.8	0.0	0.8
Unrealized Loss on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.0		0.0
Other comprehensive loss before reclassifications	(1.0)		(1.0)
Amounts reclassified to net loss	0.4		0.4
Ending balance	(0.6)		(0.6)
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	3.2	(3.8)	5.5	(1.2)
Other comprehensive income (loss)	(2.5)	0.2	(4.8)	(2.4)
Ending balance	$ 0.7	$ (3.6)	$ 0.7	$ (3.6)