Supplemental Cash Flow Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Supplemental Cash Flow Information [Abstract]
Cash paid for interest, expensed	$ 117,442,000		$ 137,950,000		$ 137,259,000
Cash paid for interest, capitalized	79,253,000		77,432,000		60,540,000
Cash paid for income taxes	28,895,000		99,194,000		45,912,000
Cash received from income tax refunds	(17,087,000)		(38,004,000)		(24,677,000)
Non-cash investing activities:
Increase in asset retirement obligations	26,946,000		56,290,000		24,694,000
Increase (decrease) in liabilities for capital expenditures	(18,321,000)		(26,882,000)		74,697,000
Increase in Restricted Cash	0		1,262,559,000	[1]	0
Decrease in Restricted Cash	1,050,328,000	[2]	212,544,000	[2]	0
Non-core Gulf Coast Assets [Member]
Business Acquisition [Line Items]
Sales proceeds paid to qualified intermediary			212,500,000
Bakken Exchange Transaction [Member]
Business Acquisition [Line Items]
Sales proceeds paid to qualified intermediary			$ 1,050,000,000

[1] During 2012, $212.5 million of proceeds from the sale of certain non-core assets in the Gulf Coast Region and $1.05 billion of the cash proceeds from the Bakken Exchange Transaction were paid by the respective purchaser directly to a qualified intermediary to facilitate a like-kind-exchange transaction for federal income tax purposes. See Note 2, Acquisitions and Divestitures, for additional details regarding these transactions.

[2] During 2012 and 2013, proceeds from the sales of our oil and natural gas property dispositions in 2012, which were held by a qualified intermediary, were released in 2012 to fund the Thompson Field acquisition and in 2013 primarily to fund a portion of the CCA acquisition and certain post-closing costs under the Bakken Exchange Transaction. See Note 2, Acquisitions and Divestitures, for additional details regarding these transactions.