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Changes in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jul. 01, 2018 | Jul. 02, 2017 | Jul. 01, 2018 | Jul. 02, 2017 | Dec. 31, 2017 | Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |
Amounts reclassified from accumulated other comprehensive income (loss), tax | $ (86) | $ (80) | $ (24) | $ (183) |  |
Foreign currency translation adjustments, tax | 0 | 0 | 0 | 0 | $ 0 | $ 0
Unrealized gains on marketable securities, tax | (511) | 1,288 | (511) | 1,288 | 1,815 | 209
Retirement plans prior service benefit, tax | (1,045) | (855) | (1,045) | (855) | $ (932) | $ (778)
Reclassification of unrealized gains on equity securities, net of tax | 68 | 42 | (11) | 106 |  |
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 Gains (Losses) on Marketable Securities |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications, tax |  |  | (744) | 1,185 |  |
Amounts reclassified from accumulated other comprehensive income (loss), tax | (68) | (42) | 11 | (106) |  |
Other comprehensive income (loss), tax |  |  | (733) | 1,079 |  |
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 | $ (18) | $ (38) | (35) | (77) |  |
Other comprehensive income (loss), tax |  |  | (35) | $ (77) |  |
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 Gains (Losses) 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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