Operating Revenues - Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Amortization period of contracts costs	10 years		10 years
Deferred contract costs amortization	$ 4.5	$ 3.3	$ 8.2	$ 6.4
Prepaid expenses and other current assets
Disaggregation of Revenue [Line Items]
Long term deferred costs	11.4		11.4		$ 9.8
Other assets
Disaggregation of Revenue [Line Items]
Long term deferred costs	$ 24.2		$ 24.2		$ 23.1