Investments in affiliates and investments in available-for-sale securities (Details) - USD ($)
$ in Thousands
 2 Months Ended 3 Months Ended 6 Months Ended
Feb. 21, 2018
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2017
Mar. 31, 2017
Mar. 20, 2017
Mar. 17, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]                      
Payments to acquire common stock               $ 6,278 $ 7,626    
Equity in net earnings of affiliated companies   $ (3,025)   $ (3,775)       (9,489) 1,307    
Investments in affiliates   174,263   189,195       174,263 189,195 $ 183,160  
Dividends received               2,919 0    
Navios Partners                      
Schedule Of Equity Method Investments [Line Items]                      
General partner interest of Navios Holdings 2.00%   2.00%   2.00% 2.00%          
Common Units issued in public offering         1,200,442            
Payments to acquire investment $ 714   $ 64   $ 110 $ 2,048          
Number of shares issued-common stock 18,422,000         47,795,000          
Equity in net earnings of affiliated companies   $ 473   473       $ 946 946    
Private placement of units to Navios Holdings     1,370,044   2,040,000            
Partners capital account units acquisitions     27,960   66,131 975,408          
Issuance of common stock $ 5,000                    
Navios Revolving Loans I Transfer | Navios Partners                      
Schedule Of Equity Method Investments [Line Items]                      
General partner interest of Navios Holdings             2.00%        
Payments to acquire investment             $ 468        
Number of shares issued-common stock             13,076,923        
Partners capital account units acquisitions             266,876        
Navios Partners                      
Schedule Of Equity Method Investments [Line Items]                      
General partner interest of Navios Holdings               2.00%      
General Partner units held by Navios Holdings   3,420,203           3,420,203      
Common units held by Navios Holdings   31,053,233           31,053,233      
Difference between carrying amount of investment and underlying equity in net assets of equity method investee   $ 84,080           $ 84,080   98,608  
Equity in net earnings of affiliated companies   5,642   2,432       9,448 3,399    
Investments in affiliates   80,364           80,364   66,773  
Dividends received   $ 690   0       $ 690 0    
Ownership percentage of Navios Holdings   20.20%           20.20%      
Market value of the investment   $ 65,155           $ 65,155      
Acropolis                      
Schedule Of Equity Method Investments [Line Items]                      
Investments in affiliates   105           105   228  
Dividends received   $ 170   55       $ 170 55    
Ownership percentage of Navios Holdings   35.00%           35.00%      
Ownership Interest               50.00%      
Profit Sharing Arrangement               Navios Holdings has a 50% interest in Acropolis, a brokerage firm for freight and shipping charters. Although Navios Holdings owns 50% of Acropolis' stock, Navios Holdings agreed with the other shareholder that the earnings and amounts declared by way of dividends will be allocated 35% to the Company with the balance to the other shareholder.      
Navios Acquisition                      
Schedule Of Equity Method Investments [Line Items]                      
Difference between carrying amount of investment and underlying equity in net assets of equity method investee   $ 116,268           $ 116,268   $ 113,597  
Equity in net earnings of affiliated companies   (9,321)   (6,507)       (20,192) (2,575)    
Investments in affiliates   76,480           76,480     $ 99,590
Dividends received   $ 1,460   $ 3,649       $ 2,919 $ 7,298    
Ownership percentage of Navios Holdings   48.30%           48.30%      
Market value of the investment   $ 44,516           $ 44,516