Regulatory Matters (Details 2) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Detail of regulatory assets
Regulatory assets, current	$ 56,158	$ 62,286
Regulatory assets, non-current	983,394	986,370
Pension and other postretirement benefits
Detail of regulatory assets
Regulatory assets, non-current	672,000	669,000
Deferred income taxes
Detail of regulatory assets
Regulatory assets, current	3,000	3,000
Regulatory assets, non-current	72,000	69,000
Deferred Fuel and Purchased Power MTM Costs
Detail of regulatory assets
Regulatory assets, current	31,000	42,000
Regulatory assets, non-current	32,000	35,000
Transmission vegetation management
Detail of regulatory assets
Regulatory assets, current	9,000
Regulatory assets, non-current	36,000	46,000
Coal reclamation
Detail of regulatory assets
Regulatory assets, current	2,000	2,000
Regulatory assets, non-current	36,000	36,000
Consolidation of VIEs
Detail of regulatory assets
Regulatory assets, non-current	34,000	33,000
Deferred compensation
Detail of regulatory assets
Regulatory assets, non-current	34,000	32,000
Tax expense of Medicare subsidy
Detail of regulatory assets
Regulatory assets, current	2,000	2,000
Regulatory assets, non-current	21,000	21,000
Loss on reacquired debt
Detail of regulatory assets
Regulatory assets, current	1,000	1,000
Regulatory assets, non-current	20,000	21,000
Pension and other post-retirement benefits deferral
Detail of regulatory assets
Regulatory assets, non-current	6,000
Demand side management
Detail of regulatory assets
Regulatory assets, current	8,000	12,000
Regulatory assets, non-current	5,000	6,000
Other.
Detail of regulatory assets
Regulatory assets, non-current	$ 15,000	$ 18,000