Lease Accounting (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) mi	Mar. 31, 2018 USD ($)
Lessor, Lease, Description [Line Items]
Operating lease costs	$ 13,200
Number of miles of pipe leased as lessor | mi	86
Fixed quarterly payments to be received under finance lease arrangement	$ 5,200
Interest rate under finance lessor arrangement	10.25%
Fair value of direct finance lease, current	$ 8,600
Marine Transportation
Lessor, Lease, Description [Line Items]
Lease revenue	6,700	$ 6,300
Onshore Facilities & Transportation
Lessor, Lease, Description [Line Items]
Lease revenue	1,600	$ 1,500
Fair value of direct finance lease, current	$ 123,335