Leases (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) mi	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating Leases [Line Items]
Operating Leases, Income Statement, Contingent Revenue	$ 24.9
Total rent expense	$ 34.8	$ 30.2	$ 25.7
Minimum [Member]
Operating Leases [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Maximum [Member]
Operating Leases [Line Items]
Lessor, Operating Lease, Term of Contract	20 years
Texas and New Mexico Pipeline (Leased) [Member]
Operating Leases [Line Items]
Pipeline, Length | mi	40