Retirement Plans and Other Postretirement Benefits - Expected Amortization Expense (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss	$ 1,173
Accretion of prior service cost	(283)
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss	225
Accretion of prior service cost	$ 0

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.

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

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- Details

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- Details

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