Debt and Letters of Credit (Details)
12 Months Ended
Dec. 31, 2014
Total Liabilities To Tangible Net Worth [Line Items]  
Applicable LIBOR Margin 1.25%
1.00 or greater  
Total Liabilities To Tangible Net Worth [Line Items]  
Applicable LIBOR Margin 1.25%
.65 or greater, but less than 1.00  
Total Liabilities To Tangible Net Worth [Line Items]  
Applicable LIBOR Margin 1.00%
Less than 0.65  
Total Liabilities To Tangible Net Worth [Line Items]  
Applicable LIBOR Margin 0.75%