Supplemental Cash Flow Information - Schedule of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Interest paid	$ 29.4	$ 23.6	$ 21.6
Non-cash investing and financing activities (included in Accounts payable):
Unpaid purchases of property and equipment	4.5	4.5	7.0
Stock repurchases not yet settled			1.3
Supplemental lease disclosures:
Operating lease liabilities arising from obtaining operating lease assets	5.4	1.8
Cash paid for amounts included in the measurement of operating lease liabilities	4.5	3.8
Finance lease liabilities arising from obtaining finance lease assets	3.2	1.0	6.5
Components of cash, cash equivalents and restricted cash:
Cash and cash equivalents	780.3	264.3	125.6
Restricted cash included in Prepaid expenses and other current assets		0.3	0.3
Restricted cash included in Other assets	14.0	14.0	13.7
Total cash, cash equivalents and restricted cash shown in our Statements of Consolidated Cash Flows	$ 794.3	$ 278.6	$ 139.6	$ 64.3