Accounting For Income Taxes (Schedule Of Deferred Income Tax Assets And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounting For Income Taxes [Abstract]
Allowance for doubtful accounts	$ 12,086	$ 12,556
Reserves not currently deductible	6,302	5,872
Net operating loss from subsidiary acquisition	14,867	6,495
Deferred compensation	3,248	3,877
Unfunded benefit obligation	80,939	54,195
Utility energy commodity derivatives	38,999	28,878
Power and natural gas deferrals	9,545	7,726
Tax credits	16,924	14,671
Other	18,838	23,226
Total deferred income tax assets	201,748	157,496
Intangible assets from subsidiary acquisition	8,334	3,505
Differences between book and tax basis of utility plant	478,604	457,661
Power deferrals		8,747
Regulatory asset for pensions and other postretirement benefits	91,125	62,645
Power exchange contract	15,571	19,966
Utility energy commodity derivatives	38,992	28,880
Loss on reacquired debt	7,193	7,979
Interest rate swaps	3,720	333
Settlement with Coeur d' Alene Tribe	19,185	21,193
Other	14,505	13,239
Total deferred income tax liabilities	677,229	624,148
Net deferred income tax liability	475,481	466,652
Current deferred income tax asset	30,473	28,822
Long-term deferred income tax liability	505,954	495,474
Net deferred income tax liability	$ (475,481)	$ (466,652)