Financial Instruments (Details 3) (Recurring basis, Interest rate swap contracts, USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Total
   
Assets    
Fair value of assets $ 664 $ 2,472
Liabilities    
Fair value of liabilities 53,420 168,508
Significant Other Observable Inputs (Level 2)
   
Assets    
Fair value of assets 664 2,472
Liabilities    
Fair value of liabilities $ 53,420 $ 168,508