Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt

The Centuri secured revolving credit and term loan facility and Centuri other debt obligations (not actively traded) are categorized as Level 3, based on significant unobservable inputs to their fair values. Because Centuri’s debt is not publicly traded, fair values for the secured revolving credit and term loan facility and other debt obligations were based on a conventional discounted cash flow methodology and utilized current market pricing yield curves, across Centuri’s debt maturity spectrum, of other industrial bonds with an assumed credit rating comparable to the Company’s.

	December 31, 2017					December 31, 2016
	Carrying Amount			Market Value		Carrying Amount			Market Value
(Thousands of dollars)
Southwest Gas Corporation:
Debentures:
Notes, 4.45%, due 2020	$	125,000		$	129,273	$	125,000		$	129,703
Notes, 6.1%, due 2041		125,000			158,304		125,000			149,734
Notes, 3.875%, due 2022		250,000			256,163		250,000			254,900
Notes, 4.875%, due 2043		250,000			283,243		250,000			266,793
Notes, 3.8%, due 2046		300,000			302,970		300,000			283,029
8% Series, due 2026		75,000			96,063		75,000			94,691
Medium-term notes, 7.59% series, due 2017		—			—		25,000			25,040
Medium-term notes, 7.78% series, due 2022		25,000			28,714		25,000			29,290
Medium-term notes, 7.92% series, due 2027		25,000			31,542		25,000			31,905
Medium-term notes, 6.76% series, due 2027		7,500			8,882		7,500			8,769
Unamortized discount and debt issuance costs		(9,350	)				(9,931	)
		1,173,150					1,197,569
Revolving credit facility and commercial paper		150,000			150,000		5,000			5,000
Industrial development revenue bonds:
Variable-rate bonds:
Tax-exempt Series A, due 2028		50,000			50,000		50,000			50,000
2003 Series A, due 2038		50,000			50,000		50,000			50,000
2008 Series A, due 2038		50,000			50,000		50,000			50,000
2009 Series A, due 2039		50,000			50,000		50,000			50,000
Unamortized discount and debt issuance costs		(2,119	)				(2,489	)
		197,881					197,511
Less: current maturities		—					(25,000	)
Long-term debt, less current maturities – Southwest Gas Corporation	$	1,521,031				$	1,375,080
Centuri:
Centuri term loan facility		199,578			207,588	$	106,700			106,819
Unamortized debt issuance costs		(1,111	)				(516	)
		198,467					106,184
Centuri secured revolving credit facility		56,472			56,525		41,185			41,292
Centuri other debt obligations		47,952			48,183		52,635			52,840
Less: current maturities		(25,346	)				(25,101	)
Long-term debt, less current maturities – Centuri	$	277,545				$	174,903
Consolidated Southwest Gas Holdings, Inc.:
Southwest Gas Corporation long-term debt	$	1,521,031				$	1,400,080
Centuri long-term debt		302,891					200,004
Less: current maturities		(25,346	)				(50,101	)
Long-term debt, less current maturities – Southwest Gas Holdings, Inc.	$	1,798,576				$	1,549,983

Summary of Effective Interest Rates on Variable-Rate IDRBs

The effective interest rates on Southwest’s variable-rate IDRBs are included in the table below:

	December 31, 2017			December 31, 2016
2003 Series A		2.44	%		1.47	%
2008 Series A		2.59	%		1.53	%
2009 Series A		2.40	%		1.43	%
Tax-exempt Series A		2.56	%		1.51	%

Estimated Maturities of Long-Term Debt

Estimated maturities of long-term debt for the next five years are (in thousands):

	Southwest		Centuri		Total
2018	$	—	$	25,346	$	25,346
2019		—		26,707		26,707
2020		125,000		27,955		152,955
2021		—		25,140		25,140
2022		425,000		194,577		619,577