Employee Benefit Plans - Summary of multi-employer benefit plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Significant multiemployer plans
Contributions to Plan	$ 102,209	$ 70,420	$ 64,888
Multiemployer Plans, Pension [Member] | Southern California IBEW-NECA Pension Trust Fund [Member]
Significant multiemployer plans
Contributions to Plan	14,268	767	435
Multiemployer Plans, Pension [Member] | National Electrical Benefit Fund [Member]
Significant multiemployer plans
Contributions to Plan	11,050	9,840	9,542
Multiemployer Plans, Pension [Member] | Eighth District Electrical Pension Fund [Member]
Significant multiemployer plans
Contributions to Plan	11,199	9,707	7,908
Multiemployer Plans, Pension [Member] | IBEW Local 769 Management Pension Plan A [Member]
Significant multiemployer plans
Contributions to Plan	2,689	2,587	2,115
Multiemployer Plans, Pension [Member] | IBEW Local No. 640 and Arizona NECA Defined Benefit Pension Plan [Member]
Significant multiemployer plans
Contributions to Plan	2,397	1,629	0
Multiemployer Plans, Pension [Member] | Indiana/Kentucky/Ohio Regional Council of Carpenters Pension Fund [Member]
Significant multiemployer plans
Contributions to Plan	1,742	1,157	2,515
Multiemployer Plans, Pension [Member] | Alaska Electrical Pension Plan [Member]
Significant multiemployer plans
Contributions to Plan	1,408	2,723	1,951
Multiemployer Plans, Postretirement Benefit [Member] | National Electrical Annuity Plan [Member]
Significant multiemployer plans
Contributions to Plan	28,822	26,559	27,633
Multiemployer Plans, Postretirement Benefit [Member] | Eighth District Electrical Pension Fund Annuity Plan [Member]
Significant multiemployer plans
Contributions to Plan	5,339	4,785	4,109
Multiemployer Plans Other Pension Post Retirement And Supplemental Plans [Member] | All other plans [Member]
Significant multiemployer plans
Contributions to Plan	$ 23,295	$ 10,666	$ 8,680