Investments in affiliates and investments in available-for-sale securities (Details) - USD ($)
$ / shares in Units, $ in Thousands
 2 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Feb. 21, 2018
Feb. 28, 2015
Sep. 30, 2018
Mar. 31, 2018
Sep. 30, 2017
Mar. 31, 2017
Mar. 20, 2017
Mar. 17, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items]                          
Payments to acquire common stock                 $ 6,278 $ 7,638 $ 7,638 $ 0 $ 22,846
Equity in net earnings of affiliated companies     $ (4,231)   $ 901       (13,720) 2,208 4,399 (202,779) 61,484
Investments in affiliates     166,888   185,548       166,888 185,548 183,160 160,071 381,746
Dividends received                 4,379 $ 3,649 7,298 0 18,244
Other than temporary impairment loss on investments                       228,026  
Navios Partners                          
Schedule Of Equity Method Investments [Line Items]                          
General partner interest of Navios Holdings 2.00%     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     $ 12      
Number of shares issued-common stock 18,422,000           47,795,000            
Equity in net earnings of affiliated companies     $ 473   473       $ 1,419 $ 1,419 $ 1,892 1,833 2,621
Private placement of units to Navios Holdings       1,370,044   2,040,000              
Partners capital account units acquisitions       27,960   66,131 975,408     7,376      
Issuance of common stock $ 5,000                        
Price per common unit             $ 2.1            
Navios Revolving Loans I Transfer                          
Schedule Of Equity Method Investments [Line Items]                          
Long-term liability recognized               $ 33,473          
Proceeds from transfer of debt               $ 4,050          
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          
Consideration equity component               $ 29,423          
Partners capital account units acquisitions               266,876          
Navios Partners                          
Schedule Of Equity Method Investments [Line Items]                          
Common Units issued in public offering   4,600,000                      
Proceeds From Issuance Of Common Limited Partners Units   $ 60,214                      
Proceeds from private placement of units to Navios Holdings   $ 14,967                      
Private placement | Common units | Navios Partners                          
Schedule Of Equity Method Investments [Line Items]                          
Private placement of units to Navios Holdings   1,120,547                      
Private placement | General partner units | Navios Partners                          
Schedule Of Equity Method Investments [Line Items]                          
Private placement of units to Navios Holdings   22,868                      
Navios Partners                          
Schedule Of Equity Method Investments [Line Items]                          
General partner interest of Navios Holdings                 2.00%   2.00%    
Payments to acquire common stock   $ 1,229                      
General Partner units held by Navios Holdings     3,420,203           3,420,203   3,016,284    
Common units held by Navios Holdings     31,053,233           31,053,233   28,421,233    
Difference between carrying amount of investment and underlying equity in net assets of equity method investee     $ 81,777           $ 81,777   $ 98,608 112,417  
Equity in net earnings of affiliated companies     4,915   3,360       14,363 $ 6,670 12,570 (5,979) 15,462
Investments in affiliates     84,116           84,116   66,773 24,033  
Dividends received     $ 690   0       $ 1,379 0 $ 0 0 27,993
Ownership percentage of Navios Holdings     20.20%           20.20%   20.80%    
Market value of the investment     $ 60,329           $ 60,329   $ 74,193    
Other than temporary impairment loss on investments                       83,596  
Acropolis                          
Schedule Of Equity Method Investments [Line Items]                          
Investments in affiliates     123           123   228 105  
Dividends received     $ 0   0       $ 170 55 $ 55 85 454
Ownership percentage of Navios Holdings     35.00%           35.00%   35.00%    
Ownership Interest                 50.00%   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 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     $ 114,741           $ 114,741   $ 113,597 140,131  
Equity in net earnings of affiliated companies     (9,856)   (2,744)       (30,048) (5,319) (9,875) 29,801 43,299
Investments in affiliates     65,164           65,164   99,590 124,062  
Dividends received     $ 1,460   $ 3,649       $ 4,379 $ 10,947 $ 14,595 14,595 $ 18,244
Ownership percentage of Navios Holdings     48.60%           48.60%   46.20%    
Percentage of voting stock of Navios Holdings in Navios Acquisition                 45.30%   42.90%    
Market value of the investment     $ 37,233           $ 37,233   $ 81,005    
Other than temporary impairment loss on investments                       $ 144,430