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Changes in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Amounts reclassified from accumulated other comprehensive income (loss), tax | $ (235) | $ (92) | $ (451)
Reclassification of unrealized gains on equity securities, net of tax | (192) | (21) | (297)
Foreign currency translation adjustments, tax | 0 | 0 | 0
Unrealized (losses) gains on marketable securities, tax | 946 | (521) | 1,815
Retirement plans prior service benefit, tax | (1,124) | (1,081) | (932)
Foreign Currency Translation Reclassification Adjustments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive income (loss) before reclassifications, tax | 0 | 0 |
Amounts reclassified from accumulated other comprehensive income (loss), tax | 0 | 0 |
Other comprehensive income (loss), tax | 0 | 0 |
Reclassification of income tax effects from the Tax Reform Act, net of tax |  | 0 |
Unrealized (Losses) Gains on Marketable Securities |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive income (loss) before reclassifications, tax | 1,659 | (722) |
Amounts reclassified from accumulated other comprehensive income (loss), tax | (192) | (21) | (297)
Other comprehensive income (loss), tax | 1,467 | (743) |
Reclassification of income tax effects from the Tax Reform Act, net of tax |  | (691) |
Amortization of Prior Service Credit |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive income (loss) before reclassifications, tax | 0 | 0 |
Amounts reclassified from accumulated other comprehensive income (loss), tax | (43) | (71) | $ (154)
Other comprehensive income (loss), tax | $ (43) | (71) |
Reclassification of income tax effects from the Tax Reform Act, net of tax |  | (78) |
ASU 2016-01 | Foreign Currency Translation Reclassification Adjustments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification of unrealized gains on equity securities, net of tax |  | 0 |
ASU 2016-01 | Unrealized (Losses) Gains on Marketable Securities |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification of unrealized gains on equity securities, net of tax |  | (902) |
ASU 2016-01 | Amortization of Prior Service Credit |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification of unrealized gains on equity securities, net of tax |  | $ 0 |

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