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Long-term Debt (Narrative) (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Senior Notes [Member]    
Debt Instrument [Line Items]    
Principal amount of debt $ 350,000,000  
Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Average interest rate during the period 2.00% 1.90%