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Assets Measured at Fair Value on Recurring Basis for Pension Plan (Detail) - Pension Plans - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | $ 91,058 | $ 87,194 | $ 86,744
Mutual Fund |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 82,230 | 77,843 |
Mutual Fund | Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 42,134 | 40,124 |
Mutual Fund | Fixed Income Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 33,924 | 32,192 |
Mutual Fund | Equity And Debt Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 6,172 | 5,527 |
Real Estate Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 8,828 | 9,351 |
Fair Value, Inputs, Level 1 | Mutual Fund |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 82,230 | 77,843 |
Fair Value, Inputs, Level 1 | Mutual Fund | Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 42,134 | 40,124 |
Fair Value, Inputs, Level 1 | Mutual Fund | Fixed Income Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | 33,924 | 32,192 |
Fair Value, Inputs, Level 1 | Mutual Fund | Equity And Debt Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets measured at fair value | $ 6,172 | $ 5,527 |

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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 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=64937038&loc=d3e12355-114930 Reference 2: 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=65897934&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Assets -URI http://asc.fasb.org/extlink&oid=6749337 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Assets -URI http://asc.fasb.org/extlink&oid=6520858 + Details
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