Revenue - Marine Segment Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Total revenue from contracts with customers	$ 439.9	$ 455.0	$ 844.8	$ 870.5
Net revenue	518.6	496.8	1,010.0	950.5
Operating Segments
Segment Reporting Information [Line Items]
Total revenue from contracts with customers	439.9	455.0	844.8	870.5
Operating Segments \| Marine Services
Segment Reporting Information [Line Items]
Total revenue from contracts with customers	39.4	68.4	81.8	105.1
Other revenue	0.0	0.0	0.0	0.0
Net revenue	39.4	68.4	81.8	105.1
Operating Segments \| Telecommunication - Maintenance \| Marine Services
Segment Reporting Information [Line Items]
Total revenue from contracts with customers	20.0	22.1	41.0	43.9
Operating Segments \| Telecommunication - Installation \| Marine Services
Segment Reporting Information [Line Items]
Total revenue from contracts with customers	10.0	16.5	15.4	23.8
Operating Segments \| Power - Operations, Maintenance & Construction Support \| Marine Services
Segment Reporting Information [Line Items]
Total revenue from contracts with customers	5.1	11.9	9.3	16.6
Operating Segments \| Power - Cable Installation & Repair \| Marine Services
Segment Reporting Information [Line Items]
Total revenue from contracts with customers	$ 4.3	$ 17.9	$ 16.1	$ 20.8

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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