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Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2019 | Apr. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance |  | $ 1,522,354 | $ 1,953,646
Other comprehensive income (loss) before reclassifications, net of tax |  | (2,559) | 7,854
Amounts reclassified from accumulated other comprehensive income (loss), net of tax |  | (107) | 0
Other comprehensive (loss) income |  | (2,666) | 9,461
Reclassification of tax effects resulting from the Tax Reform Act, net of tax | [1] |  | 769
Less: reclassification adjustment for gains included in net income, net of tax |  | (70) | 1,668
Balance |  | 1,470,228 | 1,904,983
ASU 2016-01 |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Less: reclassification adjustment for gains included in net income, net of tax | [2] |  | (3,125)
Foreign Currency Translation Reclassification Adjustments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance |  | (12,523) | 15,919
Other comprehensive income (loss) before reclassifications, net of tax |  | (4,659) | 10,541
Other comprehensive (loss) income |  | (4,659) | 10,541
Balance |  | (17,182) | 26,460
Unrealized Gains (Losses) on Marketable Securities |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance |  | (1,845) | 1,362
Other comprehensive income (loss) before reclassifications, net of tax |  | 2,100 | (2,687)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax |  | (70) | 1,668
Other comprehensive (loss) income |  | 2,030 | (1,019)
Reclassification of tax effects resulting from the Tax Reform Act, net of tax | [1] |  | 691
Balance |  | 185 | (2,091)
Unrealized Gains (Losses) on Marketable Securities | ASU 2016-01 |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Less: reclassification adjustment for gains included in net income, net of tax | [2] |  | (3,125)
Amortization of Prior Service Credit |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance |  | 1,328 | 1,495
Amounts reclassified from accumulated other comprehensive income (loss), net of tax | [3] | (37) | (61)
Other comprehensive (loss) income |  | (37) | (61)
Reclassification of tax effects resulting from the Tax Reform Act, net of tax | [1] |  | 78
Balance |  | 1,291 | 1,512
Accumulated Other Comprehensive Income (Loss) |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance |  | (13,040) | 18,776
Amounts reclassified from accumulated other comprehensive income (loss), net of tax |  | (107) | (769)
Less: reclassification adjustment for gains included in net income, net of tax |  | (70) | 1,668
Balance |  | $ (15,706) | $ 25,881
[1] | In the three months ended April 1, 2018, Teradyne early adopted the ASU 2018-02, “Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” As a result, the stranded tax effects resulting from the Tax Reform Act enacted in December 2017 were reclassified from accumulated other comprehensive income to retained earnings.
[2] | In the three months ended April 1, 2018, Teradyne adopted the ASU 2016-01, “Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities.”
[3] | The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit. See Note R: “Retirement Plans.”

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