Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 87,684	$ 70,533	$ 149,790	$ 125,676
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	176,247	166,418	233,251	218,269
Deferred income taxes	43,704	33,343	76,641	62,320
Changes in current assets and liabilities:
Accounts receivable, net of allowances	41,310	57,498	(3,855)	(32,172)
Accrued utility revenue	40,700	40,100	(1,100)	1,100
Deferred purchased gas costs	(78,709)	52,850	(108,736)	29,301
Accounts payable	(54,817)	(93,608)	12,793	(11,845)
Accrued taxes	(1,240)	(938)	(189)	645
Other current assets and liabilities	27,793	20,785	(11,940)	2,609
Gains on sale	(2,990)	(4,506)	(6,524)	(5,853)
Changes in undistributed stock compensation	5,444	4,215	6,366	6,062
AFUDC and property-related changes	(1,658)	(1,289)	(2,312)	(1,824)
Changes in other assets and deferred charges	(22,454)	(12,733)	(25,088)	(9,242)
Changes in other liabilities and deferred credits	7,524	(2,352)	5,449	(47,021)
Net cash provided by operating activities	268,538	330,316	324,546	338,025
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(254,437)	(275,970)	(374,179)	(393,335)
Restricted cash		12,785		37,783
Changes in customer advances	5,203	(21,210)	23,388	(24,217)
Miscellaneous inflows	6,407	8,767	11,603	12,650
Miscellaneous outflows		(2,004)		(2,004)
Net cash used in investing activities	(242,827)	(277,632)	(339,188)	(369,123)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	1,446	1,459	1,568	4,133
Dividends paid	(44,238)	(39,428)	(57,850)	(51,597)
Interest rate swap settlement		(21,754)		(21,754)
Issuance of long-term debt, net	63,673	453,638	99,553	515,424
Retirement of long-term debt	(130,269)	(377,457)	(179,855)	(432,865)
Change in credit facility and commercial paper	39,000	(69,000)	110,000	20,000
Change in short-term debt	33,000		33,000
Net cash provided by (used in) financing activities	(37,388)	(52,542)	6,416	33,341
Change in cash and cash equivalents	(11,677)	142	(8,226)	2,243
Cash and cash equivalents at beginning of period	25,530	21,937	22,079	19,836
Cash and cash equivalents at end of period	13,853	22,079	13,853	22,079
Supplemental information:
Interest paid, net of amounts capitalized	41,161	70,522	58,078	89,555
Income taxes paid	$ 4,929	$ 1,971	$ 5,801	$ 2,050