Revenue From Contracts With Customers - Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 1.9		$ 1.9		$ 0.7
Contract liabilities	12.8		12.8		19.9
Revenue recognized	3.4	$ 4.0	8.8	$ 7.4
Deferred contract costs	26.1		26.1		$ 42.9
Amortization of deferred contract costs	$ 9.2	$ 7.7	$ 27.2	$ 23.6