Annual report pursuant to Section 13 and 15(d)

Nature Of Operations And Accounting Policies (Narrative) (Details)

v3.20.4
Nature Of Operations And Accounting Policies (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Aug. 02, 2019
Dec. 31, 2020
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Feb. 26, 2021
Dec. 18, 2020
Jan. 01, 2019
Jan. 01, 2018
Nature of Operations and Accounting Policies [Line Items]                                
Operating revenues   $ 213,531 $ 175,414 $ 172,585 $ 192,296 $ 192,761 $ 200,658 $ 197,023 $ 209,524 $ 753,826 $ 799,966 $ 835,750        
Common stock, par value (in dollars per share)   $ 0.01               $ 0.01            
Tender Offer Price                           $ 41.50    
Payments to noncontrolling interests                   $ 0 107,692 29        
Cumulative effect of new accounting principle                             $ 25,359 $ (2,467)
Depreciation                   66,500 65,000 69,900        
Capitalized interest                   400 100 200        
Construction in progress, gross   $ 25,100               25,100            
Amortization expense                   $ 4,062 $ 3,555 4,700        
Equity method investment, other than temporary impairment                       $ 100        
Subsequent Event                                
Nature of Operations and Accounting Policies [Line Items]                                
Percentage of Common Stock Outstanding Required to be Tendered                         66.67%      
Minimum                                
Nature of Operations and Accounting Policies [Line Items]                                
Finite-lived intangible asset, useful life                   1 year            
Maximum                                
Nature of Operations and Accounting Policies [Line Items]                                
Finite-lived intangible asset, useful life                   15 years            
Accounting Standards Update 2016-02                                
Nature of Operations and Accounting Policies [Line Items]                                
Cumulative effect of new accounting principle                             175,000  
Accounting Standards Update 2016-02 | Retained Earnings                                
Nature of Operations and Accounting Policies [Line Items]                                
Cumulative effect of new accounting principle                             15,523  
Accounting Standards Update 2016-02 | Retained Earnings | Sale Leaseback                                
Nature of Operations and Accounting Policies [Line Items]                                
Cumulative effect of new accounting principle                             $ 25,400  
Accounting Standards Update 2016-16 | Retained Earnings                                
Nature of Operations and Accounting Policies [Line Items]                                
Cumulative effect of new accounting principle                               $ (2,467)
SEA-Vista                                
Nature of Operations and Accounting Policies [Line Items]                                
Stock issued during period, shares, acquisitions 1,500,000                              
Payments to noncontrolling interests $ 107,700                              
Dry-Cargo Barge Operations                                
Nature of Operations and Accounting Policies [Line Items]                                
Noncontrolling interest, ownership percentage by parent   50.00%               50.00%            
Inland River Towboat Operations                                
Nature of Operations and Accounting Policies [Line Items]                                
Noncontrolling interest, ownership percentage by parent   63.00%               63.00%            
Inland Grain Terminals/Elevators                                
Nature of Operations and Accounting Policies [Line Items]                                
Noncontrolling interest, ownership percentage by parent   50.00%               50.00%            
SEA-Vista | SEA-Vista                                
Nature of Operations and Accounting Policies [Line Items]                                
Noncontrolling interest, ownership percentage by noncontrolling owners 49.00%                              
U.S. Federal Government                                
Nature of Operations and Accounting Policies [Line Items]                                
Operating revenues                   $ 76,600            
U.S. Federal Government | Customer Concentration Risk                                
Nature of Operations and Accounting Policies [Line Items]                                
Percentage of operating revenues                   10.00%            
Ocean Services                                
Nature of Operations and Accounting Policies [Line Items]                                
Percentage of operating revenues                   51.00% 53.00% 50.00%        
Operating revenues                   $ 381,255 $ 423,288 $ 414,844        
Inland Services                                
Nature of Operations and Accounting Policies [Line Items]                                
Percentage of operating revenues                   36.00% 33.00% 34.00%        
Operating revenues                   $ 271,889 $ 267,334 $ 285,688        
Witt O'Brien's LLC                                
Nature of Operations and Accounting Policies [Line Items]                                
Percentage of operating revenues                   12.00% 13.00% 16.00%        
Operating revenues                   $ 92,416 $ 101,663 $ 131,629