Employee Benefit Plans - Summary of Plan Information Relating to Participation in Multiemployer Pension Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Multiemployer Plans [Line Items]
Contributions	$ 110,082	$ 85,235	$ 77,015
National Electrical Benefit Fund
Multiemployer Plans [Line Items]
Contributions	29,161	22,912	21,200
Pipeline Industry Pension Fund
Multiemployer Plans [Line Items]
Contributions	13,585	6,954	6,087
Central Pension Fund of the IUOE & Participating Employers
Multiemployer Plans [Line Items]
Contributions	12,176	5,668	5,677
Teamsters National Pipe Line Pension Plan
Multiemployer Plans [Line Items]
Contributions	3,602	1,661	1,343
Laborers Pension Trust Fund for Northern California
Multiemployer Plans [Line Items]
Contributions	3,387	3,805	2,603
Eighth District Electrical Pension Fund
Multiemployer Plans [Line Items]
Contributions	3,208	3,089	2,544
Laborers National Pension Fund
Multiemployer Plans [Line Items]
Contributions	3,049	1,358	7,671
Alaska Electrical Pension Plan
Multiemployer Plans [Line Items]
Contributions	2,143	2,701	639
Operating Engineers Local 324 Pension Fund
Multiemployer Plans [Line Items]
Contributions	1,969	1,291	1,231
OE Pension Trust Fund
Multiemployer Plans [Line Items]
Contributions	1,703	1,508	1,264
Plumbers and Pipefitters National Pension Fund
Multiemployer Plans [Line Items]
Contributions	1,273	1,666	850
Alaska Laborers - Employers Retirement Fund
Multiemployer Plans [Line Items]
Contributions	536	1,216	181
Laborers District Council of W PA Pension Fund
Multiemployer Plans [Line Items]
Contributions	418	876	21
Alaska Teamster Employer Pension Plan
Multiemployer Plans [Line Items]
Contributions	255	659	513
Midwest Operating Engineers Pension Trust Fund
Multiemployer Plans [Line Items]
Contributions	106	793	3,294
All other plans, US
Multiemployer Plans [Line Items]
Contributions	24,234	28,516	20,594
All other plans, Canada
Multiemployer Plans [Line Items]
Contributions	$ 9,277	$ 562	$ 1,303