Business Segment Information - Intercompany Segment Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net revenues	$ (212,609)	$ (212,575)	$ (581,160)	$ (581,462)
Well Intervention
Segment Reporting Information [Line Items]
Net revenues	(170,206)	(154,441)	(451,511)	(445,769)
Robotics
Segment Reporting Information [Line Items]
Net revenues	(51,909)	(54,340)	(136,396)	(120,569)
Intercompany Eliminations
Segment Reporting Information [Line Items]
Net revenues	23,283	12,083	51,398	33,417
Intercompany Eliminations | Well Intervention
Segment Reporting Information [Line Items]
Net revenues	15,318	4,379	28,355	10,546
Intercompany Eliminations | Well Intervention | Droshky Prospect
Segment Reporting Information [Line Items]
Net revenues	10,600		15,900
Intercompany Eliminations | Robotics
Segment Reporting Information [Line Items]
Net revenues	$ 7,965	$ 7,704	$ 23,043	$ 22,871