Long-Term Debt Credit Facility Available Borrowing Capacity (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Oct. 22, 2014 Subsequent Event [Member]		Sep. 30, 2014 Line of Credit [Member]	Oct. 06, 2014 Line of Credit [Member] Subsequent Event [Member]
Line of Credit Facility [Line Items]
Borrowing Base, Line of Credit							$ 2,200,000,000	$ 2,400,000,000
Line of Credit Facility, Amount Outstanding	390,000,000		0		558,500,000
Letters of Credit Outstanding, Amount	808,000	[1]	808,000	[1]	808,000	[1]
Line of Credit Facility, Remaining Borrowing Capacity	$ 909,192,000		$ 1,299,192,000		$ 740,692,000

[1] (1) Letters of credit reduce the available borrowing capacity under the credit facility on a dollar-for-dollar basis.