Fixed Assets and Asset Retirement Obligations Fixed Assets and Asset Retirement Obligations (Forecast of Accretion Expense) (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Forecast of Future Accretion Expense [Abstract]
Asset Retirement Obligation, Future Payments Due, Next Twelve Months	$ 7,743
Asset Retirement Obligation, Future Payments Due In Two Years	6,722
Asset Retirement Obligation, Future Payments Due In Three Years	5,141
Asset Retirement Obligation, Future Payments Due In Four Years	5,518
Asset Retirement Obligation, Future Payments Due in Five Years	$ 5,924