Revenue Costs to obtain or fulfill a contract (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Revenue Recognition [Abstract]
Costs to fulfill a contract	$ 12.7	$ 12.7
Amortization of costs to fulfill a contract	$ 2.6	$ 5.1