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Employee Benefit Plans - Participation in Multiemployer Defined Benefit Pension Plan (Details) - USD ($) $ in Thousands | 12 Months Ended
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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 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 + Details
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