Employee Benefits - Multiemployer Plans (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
International Union of Operating Engineers - Employers Construction Industry Retirement Plan - Local 302 and 612 Trust Funds
Multiemployer Plans [Line Items]
Certified Zone Status	Green	Green
Contributions	$ 2,480	$ 3,021	$ 2,482
Washington Laborers
Multiemployer Plans [Line Items]
Certified Zone Status	Green	Green
Contributions	$ 236	$ 30
Carpenters Retirement Plan of Western Washington
Multiemployer Plans [Line Items]
Certified Zone Status	Green	Green
Contributions	$ 1,898	$ 695	932
Cement Masons & Plasterers Trust Funds
Multiemployer Plans [Line Items]
Certified Zone Status	Green	Green
Contributions	$ 39	$ 2
Washington-Idaho-Montana Carpenters-Employers Retirement Trust Fund
Multiemployer Plans [Line Items]
Certified Zone Status	Yellow	Yellow
Contributions		$ 36
Engineers - AGC Retirement Trust of the Inland Empire
Multiemployer Plans [Line Items]
Certified Zone Status	Yellow	Yellow
Contributions		$ 20
Western Conference of Teamsters Pension Trust Fund
Multiemployer Plans [Line Items]
Certified Zone Status	Green	Green
Contributions	$ 15
Alaska Carpenters Trust Fund
Multiemployer Plans [Line Items]
Certified Zone Status	Yellow	Yellow
Contributions	$ 271	$ 377	328
Alaska Laborers Trust Fund
Multiemployer Plans [Line Items]
Certified Zone Status	Yellow	Yellow
Contributions	$ 226	$ 552	$ 321

Indicates certified zone status of multiemployer pension plan determined to be individually significant. Acceptable values are "Green", "Yellow", "Orange", "Red", "Other", and "NA".

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948

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- Definition

Amount of cost for employer contribution to multiemployer pension plan determined to be individually significant.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (e)(1)
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

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.

+ References

No definition available.

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