Operations by Business Segment and Geographic Area Operations by Business Segment and Geographic Area - Other Significant Reconciling Items (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	$ 104,958	$ 142,513	$ 423,988
Oil And Gas [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	101,331	136,520	413,141
ROVs [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	40,425	50,339	57,558
Subsea Products [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	27,711	56,669	69,434
Subsea Projects [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	29,544	25,602	276,308
Asset Integrity [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	3,651	3,910	9,841
Advanced Technologies [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	2,063	2,742	5,015
Corporate and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Additions	$ 1,564	$ 3,251	$ 5,832