Impairment Loss (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2013
item
Dec. 31, 2012
Jul. 16, 2014
item
Impairment Loss        
Impairment loss $ 75,776 $ 19,004 $ 129,630  
Number of vessels sold   7    
Vessel        
Impairment Loss        
Impairment loss (75,776) 0 129,600  
Number of vessels on which impairment loss is recorded 8 0 13  
Number of vessels whose charterparties were revised 8      
ZIM        
Impairment Loss        
Impairment loss   19,000    
Number of vessels whose charterparties were revised 6     6
Unsecured notes maturity term 9 years      
Receivable   $ 25,765