Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities:
Net income	$ 112,294	$ 78,800	$ 103,539
Non-cash items included in net income:
Depreciation and amortization	133,189	126,402	113,600
Provision for deferred income taxes	23,532	21,449	24,007
Power and natural gas cost amortizations (deferrals), net	(9,408)	6,702	21,870
Amortization of debt expense	3,813	3,803	4,617
Amortization of investment in exchange power	2,450	2,450	2,450
Stock-based compensation expense	6,218	5,792	5,756
Equity-related AFUDC	(6,066)	(4,055)	(2,225)
Pension and other postretirement benefit expense	42,067	39,838	32,067
Amortization of Spokane Energy contract	11,414	10,492	9,645
Write-off of Reardan wind generation capitalized costs	2,534	0	0
Other	12,982	5,256	(4,988)
Contributions to defined benefit pension plan	(44,263)	(44,000)	(26,000)
Changes in certain current assets and liabilities:
Accounts and notes receivable	(32,675)	8,100	30,616
Materials and supplies, fuel stock and natural gas stored	2,509	4,551	(3,388)
Other current assets	(18,471)	27,258	(23,881)
Accounts payable	(8,389)	30,189	(18,032)
Other current liabilities	8,827	(6,474)	(188)
Net cash provided by operating activities	242,557	316,553	269,465
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(294,363)	(271,187)	(239,782)
Other capital expenditures	(8,750)	(4,787)	(3,590)
Federal grant payments received	3,409	8,277	16,928
Cash paid by subsidiaries for acquisitions, net of cash received	0	(50,310)	(31,409)
Decrease (increase) in funds held for clients	1,815	(6,811)	78,561
Purchase of securities available for sale	(35,949)	(100,374)	(96,634)
Sale and maturity of securities available for sale	22,960	137,999	80
Other	(1,339)	(7,475)	(6,435)
Net cash used in investing activities	(312,217)	(294,668)	(282,281)
Financing Activities:
Net increase (decrease) in short-term borrowings	119,000	(9,000)	(49,000)
Borrowings from Ecova line of credit	3,000	33,000	35,000
Repayment of borrowings from Ecova line of credit	(11,000)	(14,000)	0
Proceeds from issuance of long-term debt	90,000	80,000	85,000
Redemption and maturity of long-term debt	(50,462)	(11,492)	(297)
Maturity of nonrecourse long-term debt of Spokane Energy	(14,965)	(13,669)	(12,463)
Long-term debt and short-term borrowing issuance costs	(531)	(764)	(4,477)
Cash received (paid) for settlement of interest rate swap agreements	2,901	(18,547)	(10,557)
Issuance of common stock	4,609	29,079	26,463
Cash dividends paid	(73,276)	(68,552)	(63,737)
Purchase of subsidiary noncontrolling interest	(4,587)	(917)	(6,179)
Increase (decrease) in client fund obligations	11,278	(30,996)	17,782
Issuance of subsidiary noncontrolling interest	480	3,714	0
Other	323	1,061	530
Net cash provided by (used in) financing activities	76,770	(21,083)	18,065
Net increase in cash and cash equivalents	7,110	802	5,249
Cash and cash equivalents at beginning of year	75,464	74,662	69,413
Cash and cash equivalents at end of year	82,574	75,464	74,662
Cash paid during the year:
Interest	75,411	74,900	69,083
Income taxes	44,772	8,069	26,451
Non-cash financing and investing activities:
Accounts payable for capital expenditures	12,723	21,331	20,629
Valuation adjustment for redeemable noncontrolling interests	10,704	(10,104)	4,059
Contingent consideration by subsidiary for acquisition	$ 0	$ 375	$ 0