Operating Revenues - Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Amortization period of contracts costs	10 years
Deferred contract costs amortization	$ 5.3	$ 3.7
Prepaid expenses and other current assets
Disaggregation of Revenue [Line Items]
Long term deferred costs	14.8		$ 13.2
Other assets
Disaggregation of Revenue [Line Items]
Long term deferred costs	$ 24.2		$ 24.2