CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 21,063	$ 6,525	$ 133,949	$ 124,741	$ 225,855		$ 194,217
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	80,139	75,370	245,009	223,251	324,995		286,522
Deferred income taxes			37,752	46,099	45,815		60,930
Changes in current assets and liabilities:
Accounts receivable, net of allowances			(42,139)	(19,615)	(76,769)		(33,818)
Accrued utility revenue			42,600	41,400	(700)		(1,200)
Deferred purchased gas costs			59,899	(36,608)	38,016		(54,797)
Accounts payable			(59,031)	(46,079)	(14,817)		14,317
Accrued taxes			17,991	(2,841)	26,075		(4,956)
Other current assets and liabilities			121,185	74,048	121,274		18,730
Gains on sale of equipment			(581)	(3,157)	(2,897)		(3,863)
Changes in undistributed stock compensation			5,789	6,067	6,618		7,492
Equity AFUDC			(3,413)	(3,179)	(4,395)		(5,772)
Changes in deferred charges and other assets			(19,174)	(15,855)	(24,370)		(11,096)
Changes in other liabilities and deferred credits			(52,018)	(9,786)	(54,996)		33,243
Net cash provided by operating activities			487,818	378,486	609,704		499,949
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions			(632,474)	(719,386)	(851,236)		(925,135)
Acquisition of businesses, net of cash acquired			(250)	(19,533)	(28,355)		(266,697)
Changes in customer advances			7,691	15,049	11,643		17,461
Other			6,520	12,862	8,811		13,376
Net cash used in investing activities			(618,513)	(711,008)	(859,137)		(1,160,995)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net			90,635	129,341	119,240		391,509
Dividends paid			(93,317)	(86,345)	(123,099)		(112,050)
Issuance of long-term debt, net			650,619	482,614	699,601		566,793
Retirement of long-term debt			(289,295)	(127,175)	(375,909)		(221,176)
Change in credit facility and commercial paper			(92,000)	0	(92,000)		0
Change in short-term debt			(157,000)	(122,000)	24,000		(1,500)
Principal payments on finance lease obligations			(151)	(161)	(202)		(387)
Withholding remittance - share-based compensation			(2,736)	(1,858)	(2,736)		(2,088)
Other			(1,445)	1,167	(3,888)		(456)
Net cash provided by financing activities			105,310	275,583	245,007		620,645
Effects of currency translation on cash and cash equivalents			(209)	58	(109)		(289)
Change in cash and cash equivalents			(25,594)	(56,881)	(4,535)		(40,690)
Cash and cash equivalents at beginning of period			49,539	85,361	28,480		69,170
Cash and cash equivalents at end of period	23,945	28,480	23,945	28,480	23,945		28,480
SUPPLEMENTAL INFORMATION:
Interest paid, net of amounts capitalized			63,743	62,165	103,836		99,159
Income taxes paid (received), net			(16,006)	371	(13,625)		(16,669)
Southwest Gas Corporation
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	(15,973)	(20,012)	79,568	86,746	155,993		146,287
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	55,942	52,372	173,865	159,327	230,158		205,594
Deferred income taxes			25,633	35,899	23,415		45,659
Changes in current assets and liabilities:
Accounts receivable, net of allowances			70,129	66,527	(7,135)		(3,436)
Accrued utility revenue			42,600	41,400	(700)		(1,200)
Deferred purchased gas costs			59,899	(36,608)	38,016		(54,797)
Accounts payable			(50,314)	(77,311)	(476)		(686)
Accrued taxes			15,914	(4,419)	29,228		(7,125)
Other current assets and liabilities			74,892	87,869	76,194		31,579
Changes in undistributed stock compensation			4,492	4,710	4,928		5,796
Equity AFUDC			(3,413)	(3,179)	(4,395)		(5,772)
Changes in deferred charges and other assets			(27,688)	(21,098)	(38,357)		(17,122)
Changes in other liabilities and deferred credits			(52,532)	(10,357)	(55,536)		19,762
Net cash provided by operating activities			413,045	329,506	451,333		364,539
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions			(525,221)	(587,405)	(716,564)		(784,237)
Changes in customer advances			7,691	15,049	11,643		17,461
Other			183	(51)	139		(1,353)
Net cash used in investing activities			(517,347)	(572,407)	(704,782)		(768,129)
CASH FLOW FROM FINANCING ACTIVITIES:
Contributions from parent			131,961	126,186	165,711		149,091
Dividends paid			(77,500)	(71,000)	(102,400)		(93,000)
Issuance of long-term debt, net			446,508	297,222	446,508		297,222
Retirement of long-term debt			(125,000)	0		$ (125,000)		$ 0
Change in credit facility and commercial paper			(92,000)	0	(92,000)		0
Change in short-term debt			(194,000)	(122,000)	(30,000)		21,000
Withholding remittance - share-based compensation			(2,736)	(1,857)	(2,737)		(2,087)
Other			(1,186)	(801)	(1,210)		(890)
Net cash provided by financing activities			86,047	227,750	258,872		371,336
Change in cash and cash equivalents			(18,255)	(15,151)	5,423		(32,254)
Cash and cash equivalents at beginning of period			40,489	31,962	16,811		49,065
Cash and cash equivalents at end of period	$ 22,234	$ 16,811	22,234	16,811	22,234		16,811
SUPPLEMENTAL INFORMATION:
Interest paid, net of amounts capitalized			57,168	51,720	94,106		82,539
Income taxes paid (received), net			$ (22,962)	$ (22)	$ (22,262)		$ (17,164)