Intangible Assets (Schedule of Components of Intangible Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 217,608	$ 230,908
Accumulated Amortization	67,114	68,306
Carrying Value	150,494	162,602
Intangibles associated with lease | Onshore Facilities & Transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	13,260
Accumulated Amortization	0	5,407
Carrying Value	0	7,853
Contract intangibles | Marine Transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	27,800	27,800
Accumulated Amortization	18,953	17,593
Carrying Value	8,847	10,207
Contract intangibles | Offshore pipeline transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	158,101	158,101
Accumulated Amortization	30,511	28,431
Carrying Value	127,590	129,670
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	31,707	31,747
Accumulated Amortization	17,650	16,875
Carrying Value	$ 14,057	$ 14,872