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Employee Benefit Plans - Participation in Multiemployer Defined Benefit Pension Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plan Disclosure [Line Items]
Contributions	$ 1,500	$ 1,200	$ 1,500
Multiemployer Plans, Pension
Defined Contribution Plan Disclosure [Line Items]
Contributions	12,586	12,638	14,534
Multiemployer Plans, Pension | Pension Trust Fund for Operating Engineers Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions	2,477	2,145	2,151
Multiemployer Plans, Pension | Laborers Pension Trust for Northern California
Defined Contribution Plan Disclosure [Line Items]
Contributions	953	1,059	966
Multiemployer Plans, Pension | Carpenter Funds Administrative Office
Defined Contribution Plan Disclosure [Line Items]
Contributions	727	636	842
Multiemployer Plans, Pension | Cement Mason Pension Trust Fund For Northern California
Defined Contribution Plan Disclosure [Line Items]
Contributions	423	311	371
Multiemployer Plans, Pension | All other funds
Defined Contribution Plan Disclosure [Line Items]
Contributions	$ 8,006	$ 8,487	$ 10,204

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- Definition

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+ References

No definition available.

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- Definition

Amount of contributions made to multiemployer plan by employer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947

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