Long-term Debt - Borrowing Availability (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term Debt	$ 2,126,729	$ 2,146,599
Letters of Credit and similar obligations outstanding, Amount	33,200
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit agreement, unused borrowing capacity	271,800
Long-term Debt	45,000	$ 0
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 350,000