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CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 28, 2026
Jun. 29, 2025
Jun. 28, 2026
Jun. 29, 2025
Statement of Comprehensive Income [Abstract]        
Consolidated net income $ 374,885 $ 78,372 $ 773,794 $ 177,269
Other comprehensive income (loss), net of tax:        
Foreign currency translation adjustment, net of tax of $0, $0, $0, and $0, respectively (11,444) 82,997 (31,377) 122,316
Available-for-sale marketable securities:        
Unrealized (losses) gains on marketable securities arising during period, net of tax of $176, $(17), $(68), and $115, respectively 1,767 (35) 227 585
Less: Reclassification adjustment for (gains) losses included in net income, net of tax of $16, $6, $12, $27, respectively 55 15 13 89
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Total 1,822 (20) 240 674
Cash flow hedges:        
Unrealized (losses) gains arising during period, net of tax of $0, $(51), $0, and $(109), respectively 0 (179) (0) (381)
Less: Reclassification adjustment for losses (gains) included in net income, net of tax of $0, $66, $0, and $(100), respectively 0 232 0 (350)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent 0 53 (0) (731)
Defined benefit post-retirement plan:        
Amortization of prior service credit, net of tax of $0, $0, $(1), and $(1), respectively (1) (2) (2) (3)
Other comprehensive income (loss) (9,623) 83,028 (31,139) 122,256
Consolidated comprehensive income 365,262 161,400 742,655 299,525
Less: comprehensive income attributable to noncontrolling interests 352 0 352 0
Total comprehensive income attributable to Teradyne $ 364,910 $ 161,400 $ 742,303 $ 299,525