Intangible Assets (Schedule Of Components Of Intangible Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 395,826	$ 395,692
Accumulated Amortization	196,677	190,805
Carrying Value	199,149	204,887
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	94,654	94,654
Accumulated Amortization	90,441	89,756
Carrying Value	4,213	4,898
Licensing agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	38,678	38,678
Accumulated Amortization	34,785	34,204
Carrying Value	3,893	4,474
Segment total
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	133,332	133,332
Accumulated Amortization	125,226	123,960
Carrying Value	8,106	9,372
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	35,430	35,430
Accumulated Amortization	34,027	33,676
Carrying Value	1,403	1,754
Intangibles associated with lease
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,260	13,260
Accumulated Amortization	4,578	4,459
Carrying Value	8,682	8,801
Segment total
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	48,690	48,690
Accumulated Amortization	38,605	38,135
Carrying Value	10,085	10,555
Marine contract intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	27,000	27,000
Accumulated Amortization	7,650	6,300
Carrying Value	19,350	20,700
Offshore pipeline contract intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	158,101	158,101
Accumulated Amortization	13,868	11,788
Carrying Value	144,233	146,313
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	28,703	28,569
Accumulated Amortization	11,328	10,622
Carrying Value	$ 17,375	$ 17,947