Nature of Operations and Basis of Presentation - Intercompany Transactions (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Centuri Construction Group Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Centuri accounts receivable for services provided to Southwest	$ 12,402	$ 10,006

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.

No definition available.

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Balance Type:	na
Period Type:	duration