Financial Instruments and Risk Management (Derivative Instruments Change in Fair Value of Level 3) (Details) (Derivative Commodity Instruments, USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Derivative Commodity Instruments
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 89,019,000		$ 65,801,000		$ 42,755,000
Realized gains	55,210,000		63,720,000		52,716,000
Unrealized gains (losses) relating to instruments held at the reporting date	(71,367,000)	[1]	22,160,000	[1]	23,980,000	[1]
Settlements during period	(54,573,000)		(62,662,000)		(53,650,000)
Balance at end of period	18,289,000		89,019,000		65,801,000
Unrealized gain (loss) on derivatives and commodity contracts	$ (7,600,000)		$ 19,900,000		$ (5,200,000)

[1] Includes $7.6 million in mark-to-market losses, $19.9 million in mark-to-market gains and $5.2 million in mark-to-market losses for the years ended December 31, 2013, 2012 and 2011, respectively.