Quarterly report pursuant to Section 13 or 15(d)

Segment Information Revenues from Contracts with Customers (Details)

v3.8.0.1
Segment Information Revenues from Contracts with Customers (Details) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Operating Revenues $ 184,824,000 $ 136,319,000
Ocean Services [Member]    
Operating Revenues 102,384,000 67,639,000
Inland Services [Member]    
Operating Revenues 55,921,000 60,574,000
Witt O'Brien's LLC [Member]    
Operating Revenues 26,432,000 8,008,000
Other Segments [Member]    
Operating Revenues 116,000 116,000
Corporate And Eliminations [Member]    
Operating Revenues (29,000) (18,000)
Voyage Charters [Member]    
Operating Revenues 16,501,000 267,000
Voyage Charters [Member] | Ocean Services [Member]    
Operating Revenues 16,501,000 267,000
Voyage Charters [Member] | Inland Services [Member]    
Operating Revenues 0 0
Voyage Charters [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 0 0
Voyage Charters [Member] | Other Segments [Member]    
Operating Revenues 0 0
Voyage Charters [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Contracts of Affreightment [Member]    
Operating Revenues 45,716,000 45,898,000
Contracts of Affreightment [Member] | Ocean Services [Member]    
Operating Revenues 5,006,000 0
Contracts of Affreightment [Member] | Inland Services [Member]    
Operating Revenues 40,710,000 45,898,000
Contracts of Affreightment [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 0 0
Contracts of Affreightment [Member] | Other Segments [Member]    
Operating Revenues 0 0
Contracts of Affreightment [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Harbor & Ocean Towing [Member]    
Operating Revenues 18,001,000 17,273,000
Harbor & Ocean Towing [Member] | Ocean Services [Member]    
Operating Revenues 18,001,000 17,273,000
Harbor & Ocean Towing [Member] | Inland Services [Member]    
Operating Revenues 0 0
Harbor & Ocean Towing [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 0 0
Harbor & Ocean Towing [Member] | Other Segments [Member]    
Operating Revenues 0 0
Harbor & Ocean Towing [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Unit Freight [Member]    
Operating Revenues 13,384,000 11,368,000
Unit Freight [Member] | Ocean Services [Member]    
Operating Revenues 13,384,000 11,368,000
Unit Freight [Member] | Inland Services [Member]    
Operating Revenues 0 0
Unit Freight [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 0 0
Unit Freight [Member] | Other Segments [Member]    
Operating Revenues 0 0
Unit Freight [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Terminal Operations [Member]    
Operating Revenues 8,561,000 8,279,000
Terminal Operations [Member] | Ocean Services [Member]    
Operating Revenues 0 0
Terminal Operations [Member] | Inland Services [Member]    
Operating Revenues 8,561,000 8,279,000
Terminal Operations [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 0 0
Terminal Operations [Member] | Other Segments [Member]    
Operating Revenues 0 0
Terminal Operations [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Fleeting Operations [Member]    
Operating Revenues 4,164,000 3,663,000
Fleeting Operations [Member] | Ocean Services [Member]    
Operating Revenues 0 0
Fleeting Operations [Member] | Inland Services [Member]    
Operating Revenues 4,164,000 3,663,000
Fleeting Operations [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 0 0
Fleeting Operations [Member] | Other Segments [Member]    
Operating Revenues 0 0
Fleeting Operations [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Time and Material Contracts [Member]    
Operating Revenues 23,625,000 4,074,000
Time and Material Contracts [Member] | Ocean Services [Member]    
Operating Revenues 0 0
Time and Material Contracts [Member] | Inland Services [Member]    
Operating Revenues 0 0
Time and Material Contracts [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 23,625,000 4,074,000
Time and Material Contracts [Member] | Other Segments [Member]    
Operating Revenues 0 0
Time and Material Contracts [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Retainer Contracts [Member]    
Operating Revenues 2,383,000 2,470,000
Retainer Contracts [Member] | Ocean Services [Member]    
Operating Revenues 0 0
Retainer Contracts [Member] | Inland Services [Member]    
Operating Revenues 0 0
Retainer Contracts [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 2,383,000 2,470,000
Retainer Contracts [Member] | Other Segments [Member]    
Operating Revenues 0 0
Retainer Contracts [Member] | Corporate And Eliminations [Member]    
Operating Revenues 0 0
Other [Member]    
Operating Revenues 1,951,000 2,485,000
Other [Member] | Ocean Services [Member]    
Operating Revenues 852,000 171,000
Other [Member] | Inland Services [Member]    
Operating Revenues 588,000 752,000
Other [Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 424,000 1,464,000
Other [Member] | Other Segments [Member]    
Operating Revenues 116,000 116,000
Other [Member] | Corporate And Eliminations [Member]    
Operating Revenues 29,000 18,000
Leasing Contracts Member]    
Operating Revenues 50,538,000 40,542,000
Leasing Contracts Member] | Ocean Services [Member]    
Operating Revenues 48,640,000 38,560,000
Leasing Contracts Member] | Inland Services [Member]    
Operating Revenues 1,898,000 1,982,000
Leasing Contracts Member] | Witt O'Brien's LLC [Member]    
Operating Revenues 0 0
Leasing Contracts Member] | Other Segments [Member]    
Operating Revenues 0 0
Leasing Contracts Member] | Corporate And Eliminations [Member]    
Operating Revenues $ 0 $ 0