Assets Held for Sale - Significant Assets Included in Assets Held for Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations $ in Thousands	Sep. 30, 2017 USD ($)
Long Lived Assets Held-for-sale [Line Items]
Less: accumulated depreciation	$ (113,894)
Total assets held for sale	107,010
South Texas Fabrication Yards
Long Lived Assets Held-for-sale [Line Items]
Less: accumulated depreciation	(113,596)
Total assets held for sale	104,507
Prospect Shipyard
Long Lived Assets Held-for-sale [Line Items]
Less: accumulated depreciation	(298)
Total assets held for sale	2,503
Land
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	5,492
Land | South Texas Fabrication Yards
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	5,492
Land | Prospect Shipyard
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	0
Buildings and improvements
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	117,582
Buildings and improvements | South Texas Fabrication Yards
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	117,582
Buildings and improvements | Prospect Shipyard
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	0
Machinery and equipment
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	96,271
Machinery and equipment | South Texas Fabrication Yards
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	93,552
Machinery and equipment | Prospect Shipyard
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	2,719
Furniture and fixtures
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	949
Furniture and fixtures | South Texas Fabrication Yards
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	867
Furniture and fixtures | Prospect Shipyard
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	82
Vehicles
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	610
Vehicles | South Texas Fabrication Yards
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	610
Vehicles | Prospect Shipyard
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	0
Other
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	0
Other | South Texas Fabrication Yards
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	0
Other | Prospect Shipyard
Long Lived Assets Held-for-sale [Line Items]
Total assets held for sale, gross	$ 0