Other Retirement Plans (Schedule of Multiemployer Pension Plans) (Details) - USD ($) $ in Millions | 12 Months Ended |
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, contributions (in dollars) | $ 37.5 | $ 72.6 | $ 99.7 |
Multiemployer plan, pension, insignificant, employer contribution, cost | $ 5 | $ 10.7 | 13.5 |
Central Pension Fund Of IUOE And Participating Employers [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 366052390 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Jan. 31, 2020 | Jan. 31, 2019 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 5.6 | $ 12.6 | 20.4 |
IBEW Local 1249 Pension Plan [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 156035161 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 2, 2021 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 3.7 | $ 3.2 | 2.2 |
Pipeline Industry Pension Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 736146433 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 2.6 | $ 9.6 | 20.7 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | true | true | |
Teamsters National Pipe Line Pension Plan [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 461102851 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 1.8 | $ 4.5 | 7.4 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | true | true | |
Laborers' District Council of Western Pennsylvania Pension Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 256135576 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | Implemented | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Yellow | Yellow | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 1.8 | $ 1.9 | 1.4 |
National Electrical Benefit Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 530181657 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 1.6 | $ 1.2 | 1.4 |
National Electrical Benefit Fund [Member] | Maximum [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | Dec. 31, 2023 | | |
West Virginia Laborers' Pension Trust Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 556026775 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Mar. 31, 2020 | Mar. 31, 2019 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 1.4 | $ 4.9 | 4.5 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | true | true | |
International Union of Operating Engineers Local 132 Pension Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 556015364 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Mar. 31, 2020 | Mar. 31, 2019 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 1.2 | $ 5 | 5.6 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | true | true | |
Midwest Operating Engineers Pension Trust Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 366140097 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer plans, pension protection act zone status, extended amortization provisions | true | true | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Yellow | |
Multiemployer plan, pension, significant, certified zone status, date | Mar. 31, 2020 | Mar. 31, 2019 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 1.1 | $ 1.8 | 1.5 |
Laborers' Local Union No. 158 Pension Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 236580323 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 0.9 | $ 1.5 | 1.5 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | true | true | |
Central Laborers Pension Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 376052379 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer plans, pension protection act zone status, extended amortization provisions | true | true | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | Implemented | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Yellow | Yellow | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 0.8 | $ 1.3 | 0.9 |
Laborers' National Pension Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 751280827 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | Implemented | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Red | Red | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 0.8 | $ 3 | 4.1 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | | true | |
Employer- Teamsters Local Nos. 175 & 505 Pension Trust Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 556021850 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer plans, pension protection act zone status, extended amortization provisions | true | true | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | Implemented | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Red | Red | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 0.6 | $ 1.7 | 1.5 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | true | true | |
Laborers District Council & Contractors Pension Fund of Ohio [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 316129964 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Dec. 31, 2019 | Dec. 31, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 0.4 | $ 1.4 | 1.8 |
Michigan Laborers Pension Fund [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 386233976 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer plans, pension protection act zone status, extended amortization provisions | | true | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | Implemented | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Yellow | Yellow | |
Multiemployer plan, pension, significant, certified zone status, date | Aug. 31, 2020 | Aug. 31, 2019 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 0.4 | $ 1.1 | 1.5 |
Laborers' Pension Fund of Roanoke, Virginia [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, employer identification number | 546111015 | | |
Multiemployer pension plans, plan number | 001 | | |
Multiemployer pension plans, collective bargaining arrangement, expiration date | May 31, 2023 | | |
Multiemployer pension plans, funding improvement plan and rehabilitation plan status | NA | | |
Multiemployer pension plans, surcharge | No | | |
Multiemployer plan, pension, significant, certified zone status [Fixed List] | Green | Green | |
Multiemployer plan, pension, significant, certified zone status, date | Sep. 30, 2019 | Sep. 30, 2018 | |
Multiemployer plan, pension, significant, employer contribution, cost | $ 0.3 | $ 1.5 | 2.5 |
Multiemployer pension plans, Company contributions greater than 5% of total plan contributions | true | true | |
Pension Plans [Member] | | | |
Multiemployer Plans [Line Items] | | | |
Multiemployer pension plans, contributions (in dollars) | $ 30 | $ 66.9 | $ 92.4 |