Lease Arrangements (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Future minimum revenue expected to be earned  
2015 $ 536,022
2016 519,260
2017 489,215
2018 445,822
2019 410,552
2020 and thereafter 1,288,014
Total future revenue $ 3,688,885
Lease Arrangements  
Term of periodic drydocking and special survey maintenance per vessel 2 years 6 months
Term of periodic drydocking and special survey maintenance per vessel for vessels less than 15 years old 5 years
Minimum  
Lease Arrangements  
Period of drydocking and special survey maintenance carried out on vessels 10 days
Maximum  
Lease Arrangements  
Age of vessels for which drydocking and special survey maintenance is carried out every 5 years 15 years
Period of drydocking and special survey maintenance carried out on vessels 15 days