v2.4.0.8
Reconciliation of Segment Information, Total Assets (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Jun. 30, 2012
Assets:      
Assets $ 12,752,928 $ 12,670,909 $ 12,597,896
Items excluded from segment assets:      
Recoverable Income Taxes 1,930 0  
Total Reportable Business Segments
     
Assets:      
Assets 11,771,465   11,416,441
Coal
     
Assets:      
Assets 5,600,934   5,445,502
Gas
     
Assets:      
Assets 6,170,531   5,970,939
All Other Segments [Member]
     
Assets:      
Assets 363,819   360,673
Excludes Gas Segment [Member]
     
Items excluded from segment assets:      
Cash and Other Investments 45,905   186,611
Intersegment Elimination [Member]
     
Assets:      
Assets 617,644   820,782
Items excluded from segment assets:      
Recoverable Income Taxes 1,930   0
Deferred Tax Assets 531,707   588,722
Bond Issuance Costs $ 38,102   $ 45,449