Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating Activities:
Net income	$ 88,317	$ 97,213
Non-cash items included in net income:
Depreciation and amortization	130,803	122,414
Provision for deferred income taxes	58,242	87,246
Power and natural gas cost amortizations (deferrals), net	8,416	11,422
Amortization of debt expense	2,440	2,595
Amortization of investment in exchange power	1,838	1,838
Stock-based compensation expense	5,809	6,261
Equity-related AFUDC	(5,012)	(6,306)
Pension and other postretirement benefit expense	27,816	29,076
Amortization of Spokane Energy contract	0	10,904
Other regulatory assets and liabilities and deferred debits and credits	(12,683)	(20,215)
Change in decoupling regulatory deferral	20,193	(24,693)
Other	(190)	5,052
Contributions to defined benefit pension plan	(22,000)	(12,000)
Cash paid for settlement of interest rate swap agreements	(11,302)	(53,966)
Cash received for settlement of interest rate swap agreements	2,479	0
Changes in certain current assets and liabilities:
Accounts and notes receivable	52,534	53,726
Materials and supplies, fuel stock and natural gas stored	(12,653)	(3,932)
Collateral posted for derivative instruments	(1,896)	(19,754)
Income taxes receivable	(4,254)	(25,222)
Other current assets	(16)	(8,486)
Accounts payable	(29,992)	(17,206)
Other current liabilities	8,624	18,151
Net cash provided by operating activities	307,513	254,118
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(287,853)	(288,072)
Issuance of notes receivable at subsidiaries	(2,800)	(9,718)
Equity and property investments made by subsidiaries	(10,899)	(8,741)
Distributions received from investments	1,915	0
Other	(2,714)	(8,422)
Net cash used in investing activities	(302,351)	(314,953)
Financing Activities:
Net increase in short-term borrowings	75,000	82,000
Proceeds from issuance of long-term debt	0	70,000
Maturity of long-term debt and capital leases	(2,465)	(92,375)
Issuance of common stock	1,490	66,756
Cash dividends paid	(69,220)	(65,172)
Other	(3,758)	(3,774)
Net cash provided by financing activities	1,047	57,435
Net increase (decrease) in cash and cash equivalents	6,209	(3,400)
Cash and cash equivalents at beginning of period	8,507	10,484
Cash and cash equivalents at end of period	$ 14,716	$ 7,084