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Employee Retirement Plans - Pension expense (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) item | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Employee Retirement Plans |  |  |
Number of regional multi-employer pension plans in which the entity participates | item | 34 |  |
Pension Expense | $ 12,766 | $ 10,543 | $ 9,280
Defined-contribution plans |  |  |
Employee Retirement Plans |  |  |
Pension Expense | 4,089 | 3,950 | 3,451
Multi-employer plans |  |  |
Employee Retirement Plans |  |  |
Pension Expense | $ 8,677 | $ 6,593 | $ 5,829

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- Definition Represents the number of regional multi-employer pension plans in which the entity participates. + References No definition available. + Details
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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. + Details
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- Definition The amount of pension benefit costs recognized during the period for (1) defined benefit plans and (2) defined contribution plans. For defined benefit plans, pension expense includes the following components: service cost, interest cost, expected return on plan assets, gain (loss) on plan assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. For defined contribution plans, the pension expense generally equals the firm's contribution to employees' accounts (if the firm contributes) during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Details
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- Details
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