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Employee Benefit Plans - Narrative (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer matching contributions | $ 2.3 | $ 1.8 | $ 1.8
Number of employees | 1,740 |  |
Entity number of employees, field personnel | 1,450 |  |
Contributions | $ 1.5 | $ 1.2 | $ 1.5
Red Zone |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Multiemployer plan, collective-bargaining arrangement, percentage of contributions required for multiple collective-bargaining arrangements | 65.00% |  |
Orange Zone |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Multiemployer plan, collective-bargaining arrangement, percentage of contributions required for multiple collective-bargaining arrangements | 80.00% |  |
Yellow Zone |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Multiemployer plan, collective-bargaining arrangement, percentage of contributions required for multiple collective-bargaining arrangements | 80.00% |  |
Yellow Zone | Minimum |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Multiemployer plan, collective-bargaining arrangement, percentage of contributions required for multiple collective-bargaining arrangements | 80.00% |  |
Union Members | Nevada, Arizona, California, and Hawaii |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Number of employees | 255 |  |
Number of employees, percent | 15.00% |  |

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- Definition Percentage of contributions required of employer under collective bargaining arrangement to total contributions required under all collective bargaining arrangements for pension and other postretirement 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
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