Discontinued Operations (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase of leased vessels		$ 46,442
Subsea Construction Marine Vessels Member
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment Included in Discontinued Operations	$ 33,000	25,800
Gain on sale of assets, disposal group accounted for as discontinued operations		18,800
Conventional Decommissioning Long-lived Assets Member
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment Included in Discontinued Operations		$ 8,800