Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Activities:
Net income	$ 78,800	$ 103,539	$ 94,948
Non-cash items included in net income:
Depreciation and amortization	126,402	113,600	107,626
Provision for deferred income taxes	21,449	24,007	37,734
Power and natural gas cost amortizations (deferrals), net	6,702	21,870	(9,795)
Amortization of debt expense	3,803	4,617	4,414
Amortization of investment in exchange power	2,450	2,450	2,450
Stock-based compensation expense	5,792	5,756	4,916
Equity-related AFUDC	(4,055)	(2,225)	(3,353)
Pension and other postretirement benefit expense	39,838	32,067	24,760
Amortization of Spokane Energy contract	10,492	9,645	8,866
Other	(5,256)	4,988	2,365
Contributions to defined benefit pension plan	(44,000)	(26,000)	(21,000)
Changes in working capital components:
Accounts and notes receivable	8,100	30,616	(19,081)
Materials and supplies, fuel stock and natural gas stored	4,551	(3,388)	(11,248)
Other current assets	27,258	(23,881)	(9,230)
Accounts payable	30,189	(18,032)	13,606
Other current liabilities	(6,474)	(188)	5,189
Net cash provided by operating activities	316,553	269,465	228,437
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(271,187)	(239,782)	(202,227)
Other capital expenditures	(4,787)	(3,590)	(2,429)
Federal grant payments received	8,277	16,928	7,585
Cash paid by subsidiaries for acquisitions, net of cash received	(50,310)	(31,409)	(3,777)
Decrease (increase) in funds held for clients	(6,811)	78,561	(48,895)
Purchase of securities available for sale	(100,374)	(96,634)	0
Sale and maturity of securities available for sale	137,999	80	0
Other	(7,475)	(6,435)	(3,480)
Net cash used in investing activities	(294,668)	(282,281)	(253,223)
Financing Activities:
Net increase (decrease) in short-term borrowings	(9,000)	(49,000)	23,000
Borrowings from Ecova line of credit	33,000	35,000	2,300
Repayment of borrowings from Ecova line of credit	(14,000)	0	(8,000)
Proceeds from issuance of long-term debt	80,000	85,000	136,365
Redemption and maturity of long-term debt	(11,492)	(297)	(110,242)
Premiums paid for the redemption of long-term debt	0	0	(10,710)
Maturity of nonrecourse long-term debt of Spokane Energy	(13,669)	(12,463)	(11,370)
Long-term debt and short-term borrowing issuance costs	(764)	(4,477)	(916)
Cash paid for settlement of interest rate swap agreements	(18,547)	(10,557)	0
Issuance of common stock	29,079	26,463	46,235
Cash dividends paid	(68,552)	(63,737)	(55,682)
Purchase of subsidiary noncontrolling interest	(917)	(6,179)	(2,593)
Increase (decrease) in client fund obligations	(30,996)	17,782	48,895
Issuance of subsidiary noncontrolling interest	3,714	0	0
Other	1,061	530	(118)
Net cash provided by (used in) financing activities	(21,083)	18,065	57,164
Net increase in cash and cash equivalents	802	5,249	32,378
Cash and cash equivalents at beginning of year	74,662	69,413	37,035
Cash and cash equivalents at end of year	75,464	74,662	69,413
Cash paid during the year:
Interest	74,900	69,083	74,195
Income taxes	8,069	26,451	14,153
Non-cash financing and investing activities:
Accounts payable for capital expenditures	21,331	20,629	8,315
Utility property acquired under capital leases	0	0	5,300
Redeemable noncontrolling interests	(10,104)	4,059	10,442
Contingent consideration by subsidiary for acquisition	$ 375	$ 0	$ 1,134