Intangible Assets/Liabilities Other Than Goodwill (Table) (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Dec. 31, 2016
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition Cost $ 190,212 [1] $ 200,610  
Accumulated amortization (77,924) (73,790)  
Write off 0 10,398  
Total Intangible assets net book value $ 112,288 116,422  
Trade name      
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition Cost   100,420 $ 100,420
Accumulated amortization   (45,156) (41,303)
Write off   0 0
Total Intangible assets net book value   55,264 59,117
Port terminal operating rights      
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition Cost   53,152 53,152
Accumulated amortization   (10,889) (10,162)
Write off   0 0
Total Intangible assets net book value   42,263 42,990
Customer relationships      
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition Cost   35,490 35,490
Accumulated amortization   (17,745) (15,971)
Write off   0 0
Total Intangible assets net book value   17,745 19,519
Favorable lease terms      
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition Cost   11,548 82,485
Accumulated amortization   0 (6,359)
Write off   (10,398) (70,937)
Total Intangible assets net book value   1,150 5,189
Total Intangible assets      
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition Cost   200,610 271,547
Accumulated amortization   (73,790) (73,795)
Write off   (10,398) (70,937)
Total Intangible assets net book value   $ 116,422 126,815
Unfavorable lease terms      
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition cost     (24,721)
Accumulated amortization     0
Write off     24,721
Total Intangible assets net book value     0
Total      
Acquired Finite Lived Intangible Assets [Line Items]      
Acquisition Cost     246,826
Accumulated amortization     (73,795)
Write off     (46,216)
Total Intangible assets net book value     $ 126,815
[1] As of both September 30, 2018 and December 31, 2017, intangible assets associated with the favorable lease terms included an amount of $1,150 related to purchase options for the vessels.