Nature of Operations and Basis of Presentation - Schedule of Other Property and Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Net cash surrender value of COLI policies	$ 101,000	$ 99,000
Other property	11,000	10,000
Total	325,449	326,743
Centuri Construction Group Inc [Member]
Investment [Line Items]
Centuri property and equipment	419,000	405,000
Centuri accumulated provision for depreciation and amortization	$ (206,000)	$ (187,000)