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Pension Plans - Fair Value of the Company's Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	$ 25,367	$ 24,435	$ 23,136
U.S. Treasury Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	3,517	3,893
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	453	1,042
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	16,667	14,814
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	4,730	4,686
Quoted Prices in Active Markets for Identical Assets (Level1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	20,637	19,749
Quoted Prices in Active Markets for Identical Assets (Level1) [Member] | U.S. Treasury Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	3,517	3,893
Quoted Prices in Active Markets for Identical Assets (Level1) [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	453	1,042
Quoted Prices in Active Markets for Identical Assets (Level1) [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	16,667	14,814
Quoted Prices in Active Markets for Identical Assets (Level1) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	4,730	4,686
Significant Observable Inputs (Level 2) [Member] | U.S. Treasury Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	4,730	4,686
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair market value of assets	$ 0	$ 0

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- Definition

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+ References

No definition available.

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ 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 (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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