Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 84,454	$ 76,942	$ 146,942	$ 137,766
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	147,919	134,422	283,608	262,372
Deferred income taxes	45,916	3,896	90,805	43,712
Changes in current assets and liabilities:
Accounts receivable, net of allowances	52,907	6,018	7,039	(33,662)
Accrued utility revenue	42,200	42,100	(700)	(200)
Deferred purchased gas costs	84,289	111,021	102,834	103,906
Accounts payable	(33,358)	(38,471)	1,622	11,704
Accrued taxes	(12,121)	7,614	(28,140)	(1,158)
Other current assets and liabilities	5,793	5,163	18,930	(17,696)
Gains on sale	(2,742)	(2,563)	(3,281)	(4,597)
Changes in undistributed stock compensation	3,514	1,512	4,916	5,719
AFUDC	(1,282)	(1,133)	(3,157)	(2,104)
Changes in other assets and deferred charges	223	(15,239)	1,296	(21,821)
Changes in other liabilities and deferred credits	(2,502)	2,954	5,407	(729)
Net cash provided by operating activities	415,210	334,236	628,121	483,212
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(264,872)	(203,640)	(549,232)	(425,094)
Acquisition of businesses, net of cash acquired	(17,000)	(9,261)	(17,000)	(199,758)
Restricted cash	0	785	0	18,667
Changes in customer advances	2,152	9,689	10,763	21,105
Miscellaneous inflows	4,126	4,892	7,588	9,443
Miscellaneous outflows	0	0	0	(1,400)
Net cash used in investing activities	(275,594)	(197,535)	(547,881)	(577,037)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	487	20,713	15,170	20,881
Dividends paid	(40,583)	(36,001)	(78,830)	(69,960)
Centuri distribution to redeemable noncontrolling interest	(99)	0	(198)	0
Issuance of long-term debt, net	96,128	93,165	138,779	344,674
Retirement of long-term debt	(52,966)	(78,409)	(162,530)	(206,848)
Change in credit facility and commercial paper	(147,500)	(120,000)	(27,500)	30,000
Change in short-term debt	(18,000)	(5,000)	0	0
Principal payments on capital lease obligations	(835)	(722)	(1,533)	(1,156)
Other	(124)	(534)	451	(1,319)
Net cash provided by (used in) financing activities	(163,492)	(126,788)	(116,191)	116,272
Effects of currency translation on cash and cash equivalents	5	(570)	(832)	(428)
Change in cash and cash equivalents	(23,871)	9,343	(36,783)	22,019
Cash and cash equivalents at beginning of period	35,997	39,566	48,909	26,890
Cash and cash equivalents at end of period	12,126	48,909	12,126	48,909
Supplemental information:
Interest paid, net of amounts capitalized	33,224	34,213	65,634	67,978
Income taxes paid	$ 4,737	$ 28,479	$ 19,483	$ 40,480