Revenue - Summary of Revenue Disaggregated by Service Type, and Contract Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 200,256	$ 196,837	$ 1,005,844	$ 937,094	$ 1,374,724	$ 1,283,934
Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	515,250	450,623	1,282,412	1,105,844	1,698,853	1,479,792
Master services agreement | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	410,283	348,274	1,021,798	832,813	1,291,397	1,101,216
Bid contract | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	104,967	102,349	260,614	273,031	407,456	378,576
Unit price contracts | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	415,404	368,918	1,006,577	948,593	1,316,404	1,286,059
Fixed price contracts | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	37,539	45,461	80,503	44,911	152,890	31,487
Time and materials contracts | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62,307	36,244	195,332	112,340	229,559	162,246
Gas infrastructure services | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	364,241	355,721	885,950	849,615	1,160,017	1,145,629
Electric power infrastructure services | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	70,610	4,666	184,277	14,062	202,844	19,304
Other | Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 80,399	$ 90,236	$ 212,185	$ 242,167	$ 335,992	$ 314,859