Property, Plant and Equipment PROPERTY PLANT AND EQUIPMENT (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011 Noble JV[Member] [Member]
Property, Plant and Equipment [Line Items]
Business Acquisition, Pro Forma Revenue			$ 6,073,904
Business Acquisition, Pro Forma Income (Loss) before Income Taxes			775,807
Business Acquisition, Pro Forma Net Income (Loss)			623,114
Basic Earnings Per Share, Pro Forma			$ 2.75
Business Acquisition, Pro Forma Earnings Per Share, Diluted			$ 2.72
Coal and other plant and equipment	3,681,051	3,414,940
Proved Oil and Gas Property, Successful Effort Method	1,670,404	1,596,838
Drilling Cost	1,937,336	1,550,297
Coal Properties And Surface Lands	1,404,056	1,164,107
Unproved Oil and Gas Property, Successful Effort Method	1,463,406	1,266,017
Gas Gathering Systems Net	1,058,008	1,006,882
Airshafts	397,466	366,054
Mine development	354,607	262,511
Property Subject to or Available for Operating Lease, Gross	393,372	529,758
Gas wells and related equipment	688,548	492,364
Prepaid Royalties	381,348	381,343
Other gas assets	126,239	82,217
Advances for Gas Exploration, Development and Production Amount	22,668	8,229
Property, Plant and Equipment, Gross	13,578,509	12,121,557
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	4,136,247	3,613,499
Total Property, Plant and Equipment-Net	9,442,262	10,190,967
Property, Plant and Equipment, Other, Net		$ 8,508,058