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Retirement Plans - Defined Benefit Plan, Fair Value of Plan Assets, Unobservable Input Reconciliation (Detail) - Bank And Insurance Investment Contracts [Member] - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of defined benefit plan assets, beginning balance | $ 51,963 | $ 45,093
Net purchases (sales) and appreciation (depreciation) of defined benefit plan assets | 4,755 | 6,870
Fair value of defined benefit plan assets, ending balance | $ 56,718 | $ 51,963

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