Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 72,732	$ 82,251	$ 131,629	$ 139,440
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	200,898	187,114	266,811	247,684
Deferred income taxes	5,961	37,690	32,580	62,625
Changes in current assets and liabilities:
Accounts receivable, net of allowances	6,570	34,679	(31,792)	(29,187)
Accrued utility revenue	41,700	40,700	(200)	(700)
Deferred purchased gas costs	131,495	(60,101)	122,257	(92,535)
Accounts payable	(38,878)	(85,514)	5,137	(3,029)
Accrued taxes	(4,427)	(16,869)	(1,131)	(14,704)
Other current assets and liabilities	8,333	43,650	(11,938)	20,941
Gains on sale	(3,019)	(5,661)	(3,529)	(6,783)
Changes in undistributed stock compensation	2,119	4,612	5,480	6,126
AFUDC	(2,011)	(1,571)	(2,435)	(2,187)
Changes in other assets and deferred charges	(14,423)	(17,420)	(18,735)	(16,685)
Changes in other liabilities and deferred credits	5,348	18,344	2,783	28,569
Net cash provided by operating activities	412,398	261,904	496,917	339,575
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(336,569)	(293,276)	(440,191)	(403,115)
Acquisition of businesses, net of cash acquired	(9,261)	0	(199,758)	0
Restricted cash	785	0	2,018	0
Changes in customer advances	14,300	13,124	21,539	15,694
Miscellaneous inflows	11,593	9,780	13,424	11,838
Miscellaneous outflows	0	0	(1,400)	0
Net cash used in investing activities	(319,152)	(270,372)	(604,368)	(375,583)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	35,419	419	35,405	608
Dividends paid	(55,060)	(49,295)	(72,040)	(64,592)
Issuance of long-term debt, net	123,816	37,719	355,325	285,336
Retirement of long-term debt	(143,325)	(21,528)	(260,952)	(28,272)
Change in credit facility and commercial paper	(53,000)	40,000	47,000	(100,000)
Change in short-term debt	(5,000)	0	0	(33,000)
Principal payments on capital lease obligations	(1,096)	0	(1,530)	0
Other	(504)	(759)	(1,002)	1,240
Net cash provided by (used in) financing activities	(98,750)	6,556	102,206	61,320
Effects of currency translation on cash and cash equivalents	(1,103)	0	(961)	0
Change in cash and cash equivalents	(6,607)	(1,912)	(6,206)	25,312
Cash and cash equivalents at beginning of period	39,566	41,077	39,165	13,853
Cash and cash equivalents at end of period	32,959	39,165	32,959	39,165
Supplemental information:
Interest paid, net of amounts capitalized	45,312	42,695	68,169	60,264
Income taxes paid	$ 39,856	$ 14,823	$ 49,280	$ 16,744