Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Activities:
Net income	$ 103,539	$ 94,948	$ 88,648
Non-cash items included in net income:
Depreciation and amortization	113,600	107,626	99,775
Provision for deferred income taxes	24,007	37,734	13,853
Power and natural gas cost amortizations (deferrals), net	21,870	(9,795)	51,359
Amortization of debt expense	4,617	4,414	5,673
Amortization of investment in exchange power	2,450	2,450	2,450
Stock-based compensation expense	5,756	4,916	2,906
Equity-related AFUDC	(2,225)	(3,353)	(3,078)
Other	38,724	35,261	26,147
Payments for settlements with Coeur d' Alene Tribe	(2,000)	(4,000)	(12,000)
Contributions to defined benefit pension plan	(26,000)	(21,000)	(48,000)
Changes in working capital components:
Accounts and notes receivable	30,616	(19,081)	14,659
Materials and supplies, fuel stock and natural gas stored	(3,388)	(11,248)	16,245
Other current assets	(23,881)	(9,230)	(3,528)
Accounts payable	(18,032)	13,606	(18,444)
Other current liabilities	(188)	5,189	22,116
Net cash provided by operating activities	269,465	228,437	258,781
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(239,782)	(202,227)	(205,384)
Other capital expenditures	(3,590)	(2,429)	(3,120)
Federal grant payments received	16,928	7,585
Cash paid by subsidiaries for acquisitions, net of cash received	(31,409)	(3,777)	(8,572)
Decrease (increase) in money market funds held for clients	78,561	(48,895)	8,507
Purchase of securities available for sale	(96,634)
Sale of securities available for sale	80
Other	(6,435)	(3,480)	(1,583)
Net cash used in investing activities	(282,281)	(253,223)	(210,152)
Financing Activities:
Net increase (decrease) in short-term borrowings	(49,000)	23,000	(159,500)
Borrowings from Ecova line of credit	35,000	2,300
Repayment of borrowings from Ecova line of credit		(8,000)
Proceeds from issuance of long-term debt	85,000	136,365	249,425
Redemption and maturity of long-term debt	(297)	(110,242)	(17,266)
Premiums paid for the redemption of long-term debt		(10,710)
Maturity of nonrecourse long-term debt of Spokane Energy	(12,463)	(11,370)
Redemption of long-term debt to affiliated trusts			(61,856)
Long-term debt and short-term borrowing issuance costs	(4,477)	(916)	(3,726)
Cash received (paid) for settlement of interest rate swap agreements	(10,557)		10,776
Issuance of common stock	26,463	46,235	2,622
Cash dividends paid	(63,737)	(55,682)	(44,360)
Purchase of subsidiary noncontrolling interest	(6,179)	(2,593)	(5,450)
Increase (decrease) in client fund obligations	17,782	48,895	(8,507)
Other	530	(118)	1,935
Net cash provided by (used in) financing activities	18,065	57,164	(35,907)
Net increase in cash and cash equivalents	5,249	32,378	12,722
Cash and cash equivalents at beginning of year	69,413	37,035	24,313
Cash and cash equivalents at end of year	74,662	69,413	37,035
Cash paid during the year:
Interest	69,083	74,195	58,756
Income taxes	26,451	14,153	22,695
Non-cash financing and investing activities:
Accounts payable for capital expenditures	20,629	8,315	8,404
Utility property acquired under capital leases		5,300
Redeemable noncontrolling interests	4,059	10,442	(400)
Contingent consideration by subsidiary for acquisition		$ 1,134