Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		$ 77,135	$ 99,045
Liability		216,032	229,790
Cash and cash equivalents		9,314	22,143	$ 10,391	$ 82,574
Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		700	800
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	[1]	(76,236)	(97,060)
Interest rate swaps		0	460
Funds held in trust account of Spokane Energy			1,600
Total		8,445	11,452
Counterparty and collateral netting, liabilities	[1]	(125,098)	(141,450)
Interest rate swaps		51,703	48,182
Total		90,934	88,340
Fair Value, Measurements, Recurring [Member] | Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	[1]	(692)	(1,349)
Derivative Asset		0	0
Counterparty and collateral netting, liabilities	[1]	(692)	(1,349)
Derivative Liability		4,743	35
Fair Value, Measurements, Recurring [Member] | Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, liabilities	[1]	0	0
Derivative Liability		23,179	23,299
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	[1]	(1,002)	(506)
Counterparty and collateral netting, liabilities	[1]	(37,272)	(29,386)
Fair Value, Measurements, Recurring [Member] | Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	[1]	(74,534)	(95,204)
Derivative Asset		899	1,525
Counterparty and collateral netting, liabilities	[1]	(87,126)	(110,714)
Derivative Liability		11,127	16,380
Fair Value, Measurements, Recurring [Member] | Power Option Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, liabilities	[1]	0	0
Derivative Liability		117	424
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	[1]	(8)	(1)
Derivative Asset		0	0
Counterparty and collateral netting, liabilities	[1]	(8)	(1)
Derivative Liability		65	20
Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	[2]	1,793	1,793
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	[2]	5,753	6,074
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Funds held in trust account of Spokane Energy			1,600
Total		7,546	9,467
Total		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	[2]	1,793	1,793
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	[2]	5,753	6,074
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps		1,002	966
Total		76,443	97,696
Interest rate swaps		88,975	77,568
Total		187,301	204,683
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		75,433	96,729
Liability		98,253	127,094
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		8	1
Liability		73	21
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total		692	1,349
Total		28,731	25,107
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		692	1,349
Liability		5,435	1,384
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability		23,179	23,299
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Power Option Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability		$ 117	$ 424

[1] The Company is permitted to net derivative assets and derivative liabilities with the same counterparty when a legally enforceable master netting agreement exists. In addition, the Company nets derivative assets and derivative liabilities against any payables and receivables for cash collateral held or placed with these same counterparties.

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