Income Taxes (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Deferred income taxes:
Total deferred income tax assets	$ (670,368,000)	$ (696,252,000)
Total deferred income tax liabilities	2,295,128,000	2,122,377,000
Total net deferred income tax liabilities	1,624,760,000	1,426,125,000
Total deferred income tax liabilities (assets)
Drilling and development costs expensed for income tax reporting	1,181,375,000	933,800,000
Tax depreciation in excess of book depreciation	923,443,000	924,229,000
Investment in Partnership	101,569,000	108,764,000
Accumulated OCI	28,597,000	81,087,000
Post-retirement benefits	(3,946,000)	(3,784,000)
Incentive compensation	(60,982,000)	(28,811,000)
Alternative minimum tax credit carryforward	(246,157,000)	(69,901,000)
Net operating loss carryforwards	(359,283,000)	(593,756,000)
Other	3,740,000	8,261,000
Total excluding valuation allowances	1,568,356,000	1,359,889,000
Valuation allowance	56,404,000	66,236,000
Total (including amounts classified as current assets of $31,005 and $15,946, respectively)	1,624,760,000	1,426,125,000
Current deferred income tax assets	31,005,000	15,946,000
Deferred assets/(liability) related to net unrealized income/loss from hedging transactions	38,700,000	88,800,000
Deferred tax asset related to other post-retirement benefits	5,300,000	3,600,000
Deferred tax asset related to pension plans	4,800,000	4,100,000
Total deferred tax asset related to the federal NOL carryforward	183,200,000
Deferred tax asset related to NOL carryforward		166,100,000	17,100,000
Increase (decrease) in deferred tax asset for uncertain tax positions related to federal operating loss carryforwards	10,600,000	(3,700,000)
NOL carryforward period		20 years	20 years
Deferred tax asset for state NOL carryforwards	118,200,000	86,000,000
Reduction in deferred tax asset for uncertain tax positions related to state NOL carryforwards	500,000	500,000
Valuation allowance pertaining to NOL carryforwards	56,400,000	66,200,000
Excess tax benefit		8,100,000	6,600,000
Tax benefits recognized as an addition to common stockholders' equity	$ 12,200,000