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Retirement Plans and Other Post-Retirement Benefits - Additional Information (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($) Age | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan retired union employees eligible age to participate in health care benefit plan | Age | 55 |  |
Defined benefit plan retired union employees eligible service period | 5 years |  |
Accumulated benefit obligation for all defined benefit pension plans | $ 584.3 | $ 537.6 |
Defined contribution plans Employees contribution | 50.00% |  |
Expense associated with Defined Contribution Plans | $ 2.3 | 2.0 | $ 2.1
Pension Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Pension settlement charge |  | 7.3 |
Pension settlement charge settled |  | $ 24.2 |
Discount rates | 3.85% | 4.43% |
Prior service cost as a component of net periodic benefit cost from accumulated other comprehensive income (loss) | $ 3.1 |  |
Actuarial net (gain) loss as a component of net periodic benefit cost from accumulated other comprehensive income (loss) | $ 0.2 |  |
Pension Benefits [Member] | Minimum [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rates | 1.90% |  |
Pension Benefits [Member] | Maximum [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rates | 4.55% |  |
Other Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rates | 3.68% | 4.18% |
Prior service cost as a component of net periodic benefit cost from accumulated other comprehensive income (loss) |  | $ 13.5 |
Actuarial net (gain) loss as a component of net periodic benefit cost from accumulated other comprehensive income (loss) |  | $ 0.3 |
Other Benefits [Member] | Minimum [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rates | 4.02% |  |
Other Benefits [Member] | Maximum [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rates | 4.21% |  |

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- Definition Defined benefit plan retired union employees eligible service period. + References No definition available. + Details
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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + 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 Amount included in accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan expected to be recognized in net periodic benefit (cost) credit for fiscal year following most recent annual statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount included in accumulated other comprehensive (income) loss for prior service cost (credit) expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(7) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(10) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of cost for defined contribution plan. + 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 + Details
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