Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Assets	$ 4,465		$ 1,324
Foreign currency derivatives, Assets			32
Interest rate swaps, Assets	5,084
Cash and cash equivalents	58,385		21,957
Securities available for sale	105,978		96,579
Funds held in trust account of Spokane Energy	1,600		1,600
Assets, Total	183,427		128,860
Energy commodity derivatives, Liabilities	86,408		98,496
Foreign currency derivatives, Liabilities	25
Interest rate swaps, Liabilities	9,241		18,895
Liabilities, Total	117,587		130,249
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	58,385		21,957
Funds held in trust account of Spokane Energy	1,600		1,600
Assets, Total	67,900		30,925
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Assets	21,369		80,571
Foreign currency derivatives, Assets			32
Interest rate swaps, Assets	5,084
Assets, Total	132,431		177,182
Energy commodity derivatives, Liabilities	103,312		177,743
Foreign currency derivatives, Liabilities	25
Interest rate swaps, Liabilities	9,241		18,895
Liabilities, Total	112,578		196,638
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Total	1,034		5,630
Liabilities, Total	22,947		18,488
Counterparty Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Assets	(16,904)	[1]	(79,247)	[1]
Assets, Total	(17,938)	[1]	(84,877)	[1]
Energy commodity derivatives, Liabilities	(16,904)	[1]	(79,247)	[1]
Liabilities, Total	(17,938)	[1]	(84,877)	[1]
Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Liabilities	2,354		1,688
Natural Gas Exchange Agreements [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Assets			956
Energy commodity derivatives, Liabilities	2,354		2,644
Natural Gas Exchange Agreements [Member] | Counterparty Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Assets			(956)	[1]
Energy commodity derivatives, Liabilities			(956)	[1]
Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Liabilities	18,572		9,910
Power Exchange Agreements [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Assets	1,034		4,674
Energy commodity derivatives, Liabilities	19,606		14,584
Power Exchange Agreements [Member] | Counterparty Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Assets	(1,034)	[1]	(4,674)	[1]
Energy commodity derivatives, Liabilities	(1,034)	[1]	(4,674)	[1]
Power Option Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Liabilities	987		1,260
Power Option Agreements [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy commodity derivatives, Liabilities	987		1,260
U.S. Government Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	78,735		74,893
U.S. Government Agency [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	78,735		74,893
Municipal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	5,364		425
Municipal [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	5,364		425
Corporate Fixed Income - Financial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	11,738		11,154
Corporate Fixed Income - Financial [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	11,738		11,154
Corporate Fixed Income - Industrial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	6,517		6,518
Corporate Fixed Income - Industrial [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	6,517		6,518
Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets	2,142	[2]	2,116	[2]
Fixed Income Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets	2,142	[2]	2,116	[2]
Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets	5,773	[2]	5,252	[2]
Equity Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets	5,773	[2]	5,252	[2]
Corporate Fixed Income - Utility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	2,114		2,092
Corporate Fixed Income - Utility [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	2,114		2,092
Certificates Of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	1,510		1,497
Certificates Of Deposit [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	$ 1,510		$ 1,497

[1] The Company is permitted to net derivative assets and derivative liabilities with the same counterparty when a legally enforceable master netting agreement exists.

[2] These assets are trading securities and are included in other intangibles, property and investments-net on the Condensed Consolidated Balance Sheets.