Revenue - Narrative (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) Segment Type Contract Customer	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of customers \| Customer	2,000,000
Number of customers party to contracts with rate components subject to negotiation (less than) \| Customer	24
Revenue earned on contracts in progress in excess of billings	$ 87,520	$ 5,768
Southwest Gas Corporation
Segment Reporting Information [Line Items]
Number of types of services provided to customers \| Type	2
Centuri
Segment Reporting Information [Line Items]
Number of types of services provided to customers \| Type	3
Number of types of agreements with customers \| Type	2
Increases due to amounts billed to customers in excess of revenue earned during the period	$ 30,000
Change in contract liability, revenue recognized	$ 9,600
Number of contracts with original duration more than one year \| Contract	15
Gas Operations
Segment Reporting Information [Line Items]
Number of operating segment \| Segment	1
Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Centuri
Segment Reporting Information [Line Items]
Revenue earned on contracts in progress in excess of billings	$ 50,600

Increases due to amounts billed to customers in excess of revenue earned during the period.

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- Definition

Number Of Customers

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- Definition

Number Of Customers Party To Contracts With Rate Components Subject To Negotiation

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- Definition

Number Of Types Of Agreements With Customers

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- Definition

Number Of Types Of Services Provided To Customers

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- Definition

Revenue Recognition, Number Of Contracts With Original Duration More Than One Year

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- Definition

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
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- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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