Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 262,708	$ 219,662
Accounts receivable and unbilled revenues, net	348,487	362,823
Available-for-sale investment and mortgage-related securities	659,400	671,358
Investment in stock of Federal Home Loan Bank of Seattle	95,152	96,022
Loans receivable held for investment, net	3,803,002	3,737,233
Loans held for sale, at lower of cost or fair value	5,351	26,005
Property, plant and equipment, net of accumulated depreciation of $2,142,040 in 2013 and $2,125,286 in 2012	3,640,308	3,594,829
Regulatory assets	874,151	864,596
Other	527,820	494,414
Goodwill	82,190	82,190
Total assets	10,298,569	10,149,132
Liabilities
Accounts payable	253,096	212,379
Interest and dividends payable	26,358	26,258
Deposit liabilities	4,312,620	4,229,916
Short-term borrowings-other than bank	133,937	83,693
Other bank borrowings	193,233	195,926
Long-term debt, net-other than bank	1,422,875	1,422,872
Deferred income taxes	459,249	439,329
Regulatory liabilities	325,527	322,074
Contributions in aid of construction	415,795	405,520
Retirement benefits liability	643,104	656,394
Other	471,217	526,613
Total liabilities	8,657,011	8,520,974
Preferred stock of subsidiaries - not subject to mandatory redemption	34,293	34,293
Commitments and contingencies (Notes 3 and 4)
Shareholders' equity
Preferred stock, no par value, authorized 10,000,000 shares; issued: none
Common stock, no par value, authorized 200,000,000 shares; issued and outstanding: 98,471,405 shares in 2013 and 97,928,403 shares in 2012	1,413,700	1,403,484
Retained earnings	220,049	216,804
Accumulated other comprehensive income (loss), net of taxes
Net unrealized gains on securities	9,933	10,761
Unrealized losses on derivatives	(701)	(760)
Retirement benefit plans	(35,716)	(36,424)
Accumulated other comprehensive income (loss), net of taxes	(26,484)	(26,423)
Total shareholders' equity	1,607,265	1,593,865
Total liabilities and shareholders' equity	$ 10,298,569	$ 10,149,132