Financial Instruments (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Derivative [Line Items]    
Interest rate 0.519%  
Debt instrument interest, effective percentage rate 2.14%  
Interest rate margin for default 1.63%  
Deferred expenses related to derivative instruments accumulated in other comprehensive income expected to reclassified in the next twelve months $ 1,100,000  
Recurring Basis    
Derivative [Line Items]    
Interest rate swap liability 1,096,000 1,719,000
Interest Rate Swap    
Derivative [Line Items]    
Derivative, Term 3 years  
Notional amount of interest rate derivatives 500,000,000  
Interest Rate Swap | Recurring Basis    
Derivative [Line Items]    
Interest expense reclassified from other comprehensive income into earnings 1,700,000  
Interest Rate Swap | Significant Observable Inputs (Level 2) | Recurring Basis    
Derivative [Line Items]    
Interest rate swap liability $ 1,096,000 $ 1,719,000