Financial Instruments (Details 6) (USD $)
12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jul. 16, 2014
item
Nonfinancial items measured at fair value on a non-recurring        
Impairment loss $ 75,776,000 $ 19,004,000 $ 129,630,000  
Vessel        
Nonfinancial items measured at fair value on a non-recurring        
Number of vessels whose charterparties were revised 8      
Impairment loss (75,776,000) 0 129,600,000  
Vessel | Carrying value        
Nonfinancial items measured at fair value on a non-recurring        
Fixed asset,net     167,800,000  
Vessel | Non-recurring basis | Total        
Nonfinancial items measured at fair value on a non-recurring        
Fixed asset,net 92,000,000      
Vessel | Non-recurring basis | Significant Other Observable Inputs (Level 2)        
Nonfinancial items measured at fair value on a non-recurring        
Fixed asset,net 92,000,000      
ZIM        
Nonfinancial items measured at fair value on a non-recurring        
Number of vessels whose charterparties were revised 6     6
Unsecured notes maturity term 9 years      
Impairment loss   $ 19,000,000