CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities:
Net income (loss)	$ 175,662	$ 208,074
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	355,538	328,809
Conservation amortization	85,847	77,551
Deferred income taxes and tax credits, net	81,899	90,828
Net unrealized (gain) loss on derivative instruments	22,957	(60,785)
AFUDC – equity	(11,266)	(10,769)
Funding of pension liability	(18,000)	(24,000)
Regulatory Assets	(83,370)	(138,096)
Other long-term assets and liabilities	8,275	30,766
Change in certain current assets and liabilities:
Accounts receivable and unbilled revenue	204,477	175,627
Materials and supplies	(2,436)	(28,448)
Fuel and gas inventory	(2,789)	(3,222)
Prepayments and other	7,391	(29,352)
Purchased gas adjustment	8,569	(10,743)
Accounts payable	(31,027)	(22,874)
Taxes payable	(30,074)	(36,411)
Other	(2,983)	23,391
Net cash provided by (used in) operating activities	768,670	570,346
Investing activities:
Construction expenditures - excluding equity AFUDC	(761,968)	(507,703)
Restricted cash	3,116	(1,391)
Other	5,796	(1,781)
Net cash provided by (used in) investing activities	(753,056)	(510,875)
Financing activities:
Change in short-term debt, net	(106,763)	12,996
Dividends paid	(17,543)	(111,592)
Proceeds from long-term debt and bonds issued	70,583	0
Other	15,999	13,479
Net cash provided by (used in) financing activities	(37,724)	(85,117)
Net increase (decrease) in cash and cash equivalents	(22,110)	(25,646)
Cash and cash equivalents at beginning of period	28,878	42,494
Cash and cash equivalents at end of period	6,768	16,848
Supplemental cash flow information:
Cash payments for interest (net of capitalized interest)	239,566	241,351
Cash payments (refunds) for income taxes	1,649	0
Accounts payable for capital expenditures eliminated from cash flows	87,456	58,278
Subsidiaries [Member]
Operating activities:
Net income (loss)	222,846	256,382
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	355,538	328,809
Conservation amortization	85,847	77,551
Deferred income taxes and tax credits, net	109,015	116,982
Net unrealized (gain) loss on derivative instruments	23,098	(57,218)
AFUDC – equity	(11,266)	(10,769)
Funding of pension liability	(18,000)	(24,000)
Regulatory Assets	(83,370)	(138,096)
Other long-term assets and liabilities	(15,734)	34,128
Change in certain current assets and liabilities:
Accounts receivable and unbilled revenue	215,674	175,733
Materials and supplies	(2,436)	(28,448)
Fuel and gas inventory	(2,789)	(3,222)
Prepayments and other	7,391	(29,352)
Purchased gas adjustment	8,569	(10,743)
Accounts payable	(31,027)	(22,874)
Taxes payable	(30,074)	(36,411)
Other	(857)	22,035
Net cash provided by (used in) operating activities	832,425	650,487
Investing activities:
Construction expenditures - excluding equity AFUDC	(677,004)	(507,703)
Restricted cash	3,116	(1,391)
Other	6,233	2,519
Net cash provided by (used in) investing activities	(667,655)	(506,575)
Financing activities:
Change in short-term debt, net	(106,763)	12,996
Dividends paid	(96,546)	(195,865)
Other	15,997	13,510
Net cash provided by (used in) financing activities	(187,312)	(169,359)
Net increase (decrease) in cash and cash equivalents	(22,542)	(25,447)
Cash and cash equivalents at beginning of period	28,481	41,856
Cash and cash equivalents at end of period	5,939	16,409
Supplemental cash flow information:
Cash payments for interest (net of capitalized interest)	160,426	162,091
Cash payments (refunds) for income taxes	3,058	0
Accounts payable for capital expenditures eliminated from cash flows	$ 87,456	$ 58,278