Business Segment Information - Total Assets By Reportable Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total assets	$ 2,362,837	$ 2,246,941
Reportable Segments [Member] | Well Intervention [Member]
Segment Reporting Information [Line Items]
Total assets	1,830,733	1,596,517
Reportable Segments [Member] | Robotics [Member]
Segment Reporting Information [Line Items]
Total assets	179,853	186,901
Reportable Segments [Member] | Production Facilities [Member]
Segment Reporting Information [Line Items]
Total assets	138,292	158,192
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Total assets	$ 213,959	$ 305,331