Lease Accounting (Narrative) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) mi	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) mi	Jun. 30, 2018 USD ($)
Lessor, Lease, Description [Line Items]
Operating lease costs	$ 13,000		$ 26,200
Number of miles of pipe leased as lessor | mi	86		86
Fixed quarterly payments to be received under finance lease arrangement	$ 5,200		$ 5,200
Interest rate under finance lessor arrangement			10.25%
Fair value of direct finance lease, current	8,800		$ 8,800
Marine Transportation
Lessor, Lease, Description [Line Items]
Lease revenue	6,700	$ 7,100	13,400	$ 13,400
Onshore Facilities & Transportation
Lessor, Lease, Description [Line Items]
Lease revenue	1,300	$ 1,600	2,900	$ 3,100
Fair value of direct finance lease, current	$ 121,275		$ 121,275