Commitments And Contingencies (Details) $ in Thousands	Oct. 29, 2020 claim	Aug. 02, 2016 claim	Feb. 16, 2016 claim	Sep. 30, 2020 USD ($) vessel claim equipment
Loss Contingencies [Line Items]
Unrecorded unconditional purchase obligation, due in remainder of 2020				$ 15,137
Unrecorded unconditional purchase obligation, due within 2021				37,506
Unrecorded unconditional purchase obligation, due within 2022				2,636
Unrecorded unconditional purchase obligation				$ 55,279
Deepwater Horizon Oil Spill Multi District Litigation
Loss Contingencies [Line Items]
Claims dismissed | claim		11	11
BELO/ORM | Subsequent Event
Loss Contingencies [Line Items]
Claims dismissed | claim	785
Claims filed | claim	2,400
BELO/NRC | Subsequent Event
Loss Contingencies [Line Items]
Claims dismissed | claim	80
Claims filed | claim	230
BP counter claims ORM and NRC
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number | claim				4
BP counterclaim ORM insurer
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number | claim				2
U.S.-flag - Harbor Tugs
Loss Contingencies [Line Items]
Number of equipment committed to purchase | equipment				4
Ocean Services
Loss Contingencies [Line Items]
Unrecorded unconditional purchase obligation, due in remainder of 2020				$ 8,424
Unrecorded unconditional purchase obligation, due within 2021				36,657
Unrecorded unconditional purchase obligation, due within 2022				2,636
Unrecorded unconditional purchase obligation				$ 47,717
Ocean Services | Foreign-flag Rail Ferries
Loss Contingencies [Line Items]
Number of equipment committed to purchase | vessel				2
Inland Services
Loss Contingencies [Line Items]
Unrecorded unconditional purchase obligation, due in remainder of 2020				$ 6,585
Unrecorded unconditional purchase obligation, due within 2021				849
Unrecorded unconditional purchase obligation, due within 2022				0
Unrecorded unconditional purchase obligation				$ 7,434
Inland Services | Inland River Dry-Cargo Barges
Loss Contingencies [Line Items]
Number of equipment committed to purchase | equipment				6
Inland Services | Inland River Towboat
Loss Contingencies [Line Items]
Number of equipment committed to purchase | vessel				1
Other Segment
Loss Contingencies [Line Items]
Unrecorded unconditional purchase obligation, due in remainder of 2020				$ 128
Unrecorded unconditional purchase obligation, due within 2021				0
Unrecorded unconditional purchase obligation, due within 2022				0
Unrecorded unconditional purchase obligation				$ 128