Multiemployer Plans (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Multiemployer Plans, Pension [Member]
Multiemployer Plans [Line Items]
Multiemployer Plan, Contributions by Employer	$ 58,722,000	$ 56,745,000	$ 44,527,000
Multiemployer Plans, Pension [Member] \| Alaska Laborers-Employers Retirement Fund [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	916028298
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Yellow	Yellow
Multiemployer Plans, Certified Zone Status, Date	Jun. 30, 2018	Jun. 30, 2017
FIP/RP Status Pending/Implemented	Implemented
Multiemployer Plan, Contributions by Employer	$ 732,000	$ 690,000	766,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Dec. 31, 2018
Multiemployer Plans, Pension [Member] \| Construction Industry and Laborers Joint Pension Trust for So Nevada, Plan A [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	880135695
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Red	Red
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	Implemented
Multiemployer Plan, Contributions by Employer	$ 346,000	$ 377,000	523,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Jun. 30, 2019
Multiemployer Plans, Pension [Member] \| Edison Pension Plan [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	936061681
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Green	Green
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	No
Multiemployer Plan, Contributions by Employer	$ 12,111,000	$ 12,725,000	6,242,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Jun. 30, 2019
Multiemployer Plans, Pension [Member] \| Local Union 212 IBEW Pension Trust Fund [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	316127280
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Green	Green
Multiemployer Plans, Certified Zone Status, Date	Apr. 30, 2018	Apr. 30, 2017
FIP/RP Status Pending/Implemented	No
Multiemployer Plan, Contributions by Employer	$ 1,341,000	$ 1,312,000	1,146,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Jun. 02, 2019
Multiemployer Plans, Pension [Member] \| IBEW Local No. 357 Pension Plan A [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	886023284
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Green	Green
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	No
Multiemployer Plan, Contributions by Employer	$ 3,460,000	$ 3,286,000	3,016,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	May 31, 2021
Multiemployer Plans, Pension [Member] \| IBEW Local 648 Pension Plan [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	316134845
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Yellow	Red
Multiemployer Plans, Certified Zone Status, Date	Feb. 28, 2018	Feb. 28, 2017
FIP/RP Status Pending/Implemented	Implemented
Multiemployer Plan, Contributions by Employer	$ 2,175,000	$ 2,254,000	773,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Aug. 29, 2021
Multiemployer Plans, Pension [Member] \| IBEW Local No. 82 Pension Plan [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	316127268
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Green	Green
Multiemployer Plans, Certified Zone Status, Date	Jun. 30, 2018	Jun. 30, 2017
FIP/RP Status Pending/Implemented	No
Multiemployer Plan, Contributions by Employer	$ 1,569,000	$ 1,757,000	2,560,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Dec. 01, 2019
Multiemployer Plans, Pension [Member] \| Idaho Plumbers and Pipefitters Pension Plan [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	826010346
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Green	Green
Multiemployer Plans, Certified Zone Status, Date	May 31, 2018	May 31, 2017
FIP/RP Status Pending/Implemented	No
Multiemployer Plan, Contributions by Employer	$ 1,247,000	$ 1,156,000	1,221,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Sep. 30, 2019
Multiemployer Plans, Pension [Member] \| Minnesota Teamsters Construction Division Pension Fund [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	416187751
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Green	Green
Multiemployer Plans, Certified Zone Status, Date	Nov. 30, 2017	Nov. 30, 2016
FIP/RP Status Pending/Implemented	No
Multiemployer Plan, Contributions by Employer	$ 740,000	$ 826,000	690,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Apr. 30, 2019
Multiemployer Plans, Pension [Member] \| National Automatic Sprinkler Industry Pension Fund [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	526054620
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Red	Red
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	Implemented
Multiemployer Plan, Contributions by Employer	$ 738,000	$ 718,000	775,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, First	Mar. 31, 2021
Expiration Date of Collective Bargaining Agreement	Jul. 31, 2024
Multiemployer Plans, Pension [Member] \| National Electrical Benefit Fund [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	530181657
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Green	Green
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	No
Multiemployer Plan, Contributions by Employer	$ 8,468,000	$ 8,891,000	6,366,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, First	Jan. 31, 2018
Expiration Date of Collective Bargaining Agreement	May 31, 2022
Multiemployer Plans, Pension [Member] \| Pension Trust Fund for Operating Engineers [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	946090764
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Yellow	Red
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	Implemented
Multiemployer Plan, Contributions by Employer	$ 2,403,000	$ 2,391,000	2,069,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, First	Jun. 15, 2019
Expiration Date of Collective Bargaining Agreement	Jun. 30, 2020
Multiemployer Plans, Pension [Member] \| Sheet Metal Workers Pension Plan of Southern CA, AZ, and NV [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	956052257
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Yellow	Yellow
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	Implemented
Multiemployer Plan, Contributions by Employer	$ 1,774,000	$ 1,016,000	1,087,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Jun. 30, 2019
Multiemployer Plans, Pension [Member] \| Southwest Marine Pension Trust [Member]
Multiemployer Plans [Line Items]
Entity tax ID number	956123404
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Red	Red
Multiemployer Plans, Certified Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	Implemented
Multiemployer Plan, Contributions by Employer	$ 81,000	$ 48,000	50,000
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Jan. 31, 2019
Multiemployer Plans, Pension [Member] \| Multiemployer Plan, Individually Insignificant Multiemployer Plans [Member]
Multiemployer Plans [Line Items]
Multiemployer Plan, Contributions by Employer	$ 21,537,000	$ 19,298,000	17,243,000
Minimum [Member]
Multiemployer Plans [Line Items]
Multiemployer plan yellow zone status funded percentage	65.00%
Multiemployer plan green zone status funded percentage	80.00%
Maximum [Member]
Multiemployer Plans [Line Items]
Multiemployer plan red zone status funded percentage	65.00%
Mulitiemployer plan yellow status funded percentage	80.00%
Withdrawal from Multiemployer Defined Benefit Plan [Member] \| Multiemployer Plans, Pension [Member] \| Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member]
Multiemployer Plans [Line Items]
Multiemployer Discounted Future Quarterly Payments			42,000
Multiemployer Withdrawal Liability Prior Accrual			16,400,000
Multiemployer Plans, Withdrawal Obligation			$ 5,200,000

The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

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Multiemployer plan green zone status funded percentage

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Amount of contributions made to multiemployer plan by employer.

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Three digit plan number for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Date of the multiemployer plan's year end to which the certified zone status relates, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire first in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire last in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Indicate whether a funding improvement plan or rehabilitation plan has been implemented or is pending for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "pending", "implemented", "other", and "NA".

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA".

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