Teradyne (TER) 10-Q 10 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 06, 2019
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Entity Registrant Name	TERADYNE, INC
Entity Central Index Key	0000097210
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Trading Symbol	TER
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		171,395,402

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019		Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 483,728		$ 926,752
Marketable securities	421,088		190,096
Accounts receivable, less allowance for doubtful accounts of $1,675 and $1,673 at March 31, 2019 and December 31, 2018, respectively	333,840		291,267
Inventories, net	161,342		153,541
Prepayments and other current assets	194,044		170,826
Total current assets	1,594,042		1,732,482
Property, plant and equipment, net	283,300		279,821
Operating lease right-of-use assets, net	50,733
Marketable securities	91,926		87,731
Deferred tax assets	69,687		70,848
Retirement plans assets	16,791		16,883
Other assets	11,279		11,509
Acquired intangible assets, net	119,372		125,482
Goodwill	379,513		381,850
Total assets	2,616,643	[1]	2,706,606
Current liabilities:
Accounts payable	118,816		100,688
Accrued employees' compensation and withholdings	89,089		148,566
Deferred revenue and customer advances	84,764		77,711
Other accrued liabilities	67,422		78,272
Contingent consideration	22,803		34,865
Operating lease liabilities	17,176
Income taxes payable	41,898		36,185
Total current liabilities	441,968		476,287
Retirement plans liabilities	121,205		117,456
Long-term deferred revenue and customer advances	32,843		32,750
Deferred tax liabilities	19,614		20,662
Long-term other accrued liabilities	9,732		37,547
Long-term contingent consideration	15,510		35,678
Long-term operating lease liabilities	38,062
Long-term incomes taxes payable	83,891		83,891
Debt	383,590		379,981
Total liabilities	1,146,415		1,184,252
Commitments and contingencies (See Note S)
SHAREHOLDERS' EQUITY
Common stock, $0.125 par value, 1,000,000 shares authorized; 172,353 and 175,522 shares issued and outstanding at March 31, 2019 and December 31, 2018, respectively	21,544		21,940
Additional paid-in capital	1,679,997		1,671,645
Accumulated other comprehensive loss	(15,706)		(13,040)
Accumulated deficit	(215,607)		(158,191)
Total shareholders' equity	1,470,228		1,522,354
Total liabilities and shareholders' equity	$ 2,616,643		$ 2,706,606
[1]	Total business assets are directly attributable to each business. Corporate assets consist of cash and cash equivalents, marketable securities and certain other assets.

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts receivable, less allowance for doubtful accounts	$ 1,675	$ 1,673
Common stock, par value	$ 0.125	$ 0.125
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	172,353,000	175,522,000
Common stock, shares outstanding	172,353,000	175,522,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Revenues:
Total revenues	$ 494,099	$ 487,467
Cost of revenues:
Total cost of revenues (exclusive of acquired intangible assets amortization shown separately below)	206,464	217,635
Gross profit	287,635	269,832
Operating expenses:
Selling and administrative	102,013	90,505
Engineering and development	76,791	74,408
Acquired intangible assets amortization	10,634	7,698
Restructuring and other	5,112	(313)
Total operating expenses	194,550	172,298
Income from operations	93,085	97,534
Non-operating (income) expense:
Interest income	(8,052)	(5,981)
Interest expense	5,713	6,890
Other (income) expense, net	1,445	805
Income before income taxes	93,979	95,820
Income tax (benefit) provision	(15,159)	8,846
Net income	$ 109,138	$ 86,974
Net income per common share:
Basic	$ 0.63	$ 0.45
Diluted	$ 0.62	$ 0.43
Weighted average common shares-basic	173,532	195,255
Weighted average common shares-diluted	176,972	203,484
Product [Member]
Revenues:
Total revenues	$ 393,442	$ 403,925
Cost of revenues:
Total cost of revenues (exclusive of acquired intangible assets amortization shown separately below)	165,368	180,958
Service [Member]
Revenues:
Total revenues	100,657	83,542
Cost of revenues:
Total cost of revenues (exclusive of acquired intangible assets amortization shown separately below)	$ 41,096	$ 36,677

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Net income	$ 109,138	$ 86,974
Other comprehensive income, net of tax:
Foreign currency translation adjustment, net of tax of $0, $0, respectively	(4,659)	10,541
Available-for-sale marketable securities:
Unrealized gains (losses) on marketable securities arising during period, net of tax of $577, $(718), respectively	2,100	(2,687)
Less: Reclassification adjustment for (gains) losses included in net income, net of tax of $(20), $78, respectively	(70)	1,668
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Total	2,030	(1,019)
Defined benefit pension and post-retirement plans:
Amortization of prior service benefit included in net periodic pension and post-retirement benefit, net of tax of $(11), $(18), respectively	(37)	(61)
Other comprehensive (loss) income	(2,666)	9,461
Comprehensive income	$ 106,472	$ 96,435

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Foreign currency translation adjustments, tax	$ 0	$ 0
Unrealized gains (losses) on marketable securities arising during period, net of tax	577	(718)
Reclassification adjustment for (gains) losses included in net income, net of tax	(20)	(78)
Amortization of prior service benefit included in net periodic pension and post-retirement benefit, net of ta	$ (11)	$ (18)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Balance at Jan. 01, 2018	$ 1,953,646	$ 24,444	$ 1,638,413	$ 18,776	$ 272,013
Balance, Shares at Jan. 01, 2018		195,548
Issuance of common stock to employees under benefit plans, net of shares withheld for payroll tax	(7,979)	$ 150	(8,129)
Issuance of common stock to employees under benefit plans, net of shares withheld for payroll tax (in shares)		1,199
Stock-based compensation expense	8,472		8,472
Repurchase of common stock	$ (140,672)	$ (368)			(140,304)
Repurchase of common stock (in shares)	2,900	(2,939)
Cash dividends ($0.09 per share)	$ (17,598)				(17,598)
Net income	86,974				86,974
Foreign currency translation adjustment	10,541			10,541
Unrealized gains (losses) on marketable securities:
Unrealized gain (loss) on marketable securities, net of tax	(2,687)			(2,687)
Less: reclassification adjustment for gains included in net income, net of tax	1,668			1,668
Reclassification of unrealized gains on equity securities, net of tax of $(902)	0			(3,125)	3,125
Amortization of prior service benefit, net of tax	(61)			(61)
Reclassification of tax effects resulting from the Tax Reform Act, net of tax of $769	0			769	(769)
Balance at Apr. 01, 2018	1,904,983	$ 24,226	1,638,756	25,881	216,120
Balance, Shares at Apr. 01, 2018		193,808
Unrealized gains (losses) on marketable securities:
Cumulative effect of changes in accounting principle related to revenue recognition	12,679				12,679
Balance at Dec. 31, 2018	1,522,354	$ 21,940	1,671,645	(13,040)	(158,191)
Balance, Shares at Dec. 31, 2018		175,522
Issuance of common stock to employees under benefit plans, net of shares withheld for payroll tax	(49)	$ 161	(210)
Issuance of common stock to employees under benefit plans, net of shares withheld for payroll tax (in shares)		1,287
Stock-based compensation expense	8,562		8,562
Repurchase of common stock	$ (151,470)	$ (557)			(150,913)
Repurchase of common stock (in shares)	4,500	(4,456)
Cash dividends ($0.09 per share)	$ (15,641)				(15,641)
Net income	109,138				109,138
Foreign currency translation adjustment	(4,659)			(4,659)
Unrealized gains (losses) on marketable securities:
Unrealized gain (loss) on marketable securities, net of tax	2,100			2,100
Less: reclassification adjustment for gains included in net income, net of tax	(70)			(70)
Amortization of prior service benefit, net of tax	(37)			(37)
Reclassification of tax effects resulting from the Tax Reform Act, net of tax of $769	107			107
Balance at Mar. 31, 2019	$ 1,470,228	$ 21,544	$ 1,679,997	$ (15,706)	$ (215,607)
Balance, Shares at Mar. 31, 2019		172,353

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Issuance of stock to employees under benefit plans, net of shares withheld for payroll tax	$ 14,318	$ 19,629
Unrealized (losses) gains on marketable securities arising during period, tax	577	(718)
Reclassification adjustment for gains included in net income, tax	20	78
Amortization of prior service benefit, net of tax	$ (11)	(18)
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings Tax Effect		$ 769
Common Stock, Dividends, Per Share, Cash Paid	$ 0.09	$ 0.09
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Reclassification adjustment for gains included in net income, tax		$ 902
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings Tax Effect		$ 691

CONDENSED CONSOLIDATED STATEM_6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Cash flows from operating activities:
Net income	$ 109,138	$ 86,974
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	16,651	16,336
Amortization	12,942	9,204
Stock-based compensation	9,474	9,544
Deferred taxes	1,206	8,696
Provision for excess and obsolete inventory	2,397	3,522
Contingent consideration fair value adjustment	2,970	(4,968)
(Gains) losses on investments	(2,828)	1,241
Other	219	152
Changes in operating assets and liabilities, net of businesses acquired:
Accounts receivable	(41,706)	(140,747)
Inventories	(2,917)	(21,017)
Prepayments and other assets	(18,648)	(679)
Accounts payable and other liabilities	(53,323)	(46,706)
Deferred revenue and customer advances	6,455	9,644
Retirement plans contributions	(1,210)	(1,020)
Income taxes	(22,804)	(12,106)
Net cash provided by (used for) operating activities	18,016	(81,930)
Cash flows from investing activities:
Purchases of property, plant and equipment	(25,711)	(34,797)
Purchases of marketable securities	(375,184)	(490,324)
Proceeds from sales of marketable securities	5,440	800,671
Proceeds from maturities of marketable securities	141,201	212,698
Proceeds from life insurance	273
Acquisition of businesses, net of cash acquired	(6,970)	(25,356)
Net cash (used for) provided by investing activities	(260,951)	462,892
Cash flows from financing activities:
Issuance of common stock under stock purchase and stock option plans	14,268	10,654
Repurchase of common stock	(156,468)	(134,276)
Dividend payments	(15,627)	(17,588)
Payments related to net settlement of employee stock compensation awards	(14,318)	(19,629)
Payments of contingent consideration	(27,615)	(13,571)
Net cash used for financing activities	(199,760)	(174,410)
Effects of exchange rate changes on cash and cash equivalents	(329)	1,478
(Decrease) increase in cash and cash equivalents	(443,024)	208,030
Cash and cash equivalents at beginning of period	926,752	429,843
Cash and cash equivalents at end of period	$ 483,728	$ 637,873

The Company

The Company	3 Months Ended
	Mar. 31, 2019
The Company	A. THE COMPANY Teradyne, Inc. (“Teradyne”) is a leading global supplier of automation equipment for test and industrial applications. Teradyne designs, develops, manufactures and sells automatic test systems used to test semiconductors, wireless products, data storage and complex electronics systems in the consumer electronics, wireless, automotive, industrial, computing, communications, and aerospace and defense industries. Teradyne’s industrial automation products include collaborative robotic arms, autonomous mobile robots, and advanced robotic control software used by global manufacturing and light industrial customers to improve quality, increase manufacturing and material handling efficiency and decrease manufacturing costs. Teradyne’s automatic test equipment and industrial automation products and services include: • semiconductor test (“Semiconductor Test”) systems; • industrial automation (“Industrial Automation”) products; • defense/aerospace (“Defense/Aerospace”) test instrumentation and systems, storage test (“Storage Test”) systems, and circuit-board test and inspection (“Production Board Test”) systems (collectively these products represent “System Test”); and • wireless test (“Wireless Test”) systems.

Accounting Policies

Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies	B. ACCOUNTING POLICIES Basis of Presentation The consolidated interim financial statements include the accounts of Teradyne and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated. These interim financial statements are unaudited and reflect all normal recurring adjustments that are, in the opinion of management, necessary for the fair statement of such interim financial statements. Certain prior year amounts were reclassified to conform to the current year presentation. The December 31, 2018 condensed consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America. The accompanying financial information should be read in conjunction with the consolidated financial statements and notes thereto contained in Teradyne’s Annual Report on Form 10-K, filed with the U.S. Securities and Exchange Commission (“SEC”) on March 1, 2019, for the year ended December 31, 2018. Preparation of Financial Statements and Use of Estimates The preparation of consolidated financial statements requires management to make estimates and judgments that affect the amounts reported in the financial statements. Actual results may differ significantly from these estimates. Leases In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, “Leases (Topic 842)” “Leases (Topic 842): Targeted Improvements,” Under ASC 842, a contract is or contains a lease when Teradyne has the right to control the use of an identified asset. Teradyne determines if an arrangement is a lease at inception of the contract, which is the date on which the terms of the contract are agreed to and the agreement creates enforceable rights and obligations. The commencement date of the lease is the date that the lessor makes an underlying asset available for use by Teradyne. As of March 31, 2019, Teradyne does not have material leases that have not yet commenced. Teradyne determines if the lease is operating or finance at the lease commencement date based upon the terms of the lease and the nature of the asset. The lease term used to calculate the lease liability includes options to extend or terminate the lease when it is reasonably certain that the option will be exercised. For leases commencing after January 1, 2019, the lease liability is measured at the present value of future lease payments, discounted using the discount rate for the lease at the commencement date. As Teradyne is typically unable to determine the implicit rate, Teradyne uses an incremental borrowing rate based on the lease term and economic environment at commencement date. Teradyne initially measures payments based on an index by using the applicable rate at lease commencement. Variable payments that do not depend on an index are not included in the lease liability and are recognized as they are incurred. The ROU asset is initially measured as the amount of lease liability, adjusted for any initial lease costs, prepaid lease payments, and reduced by any lease incentives. Teradyne’s contracts often include non-lease components such as common area maintenance. Teradyne elected the practical expedient to account for the lease and non-lease components as a single lease component. For leases with a term of one year or less Teradyne has elected not to record the lease asset or liability. The lease payments are recognized in the consolidated statement of earnings on a straight-line basis over the lease term. Teradyne includes lease costs within cost of revenues and operating expenses. See Note: H: “Leases.”

Recently Issued Accounting Pron

Recently Issued Accounting Pronouncements	3 Months Ended
	Mar. 31, 2019
Recently Issued Accounting Pronouncements	C. RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS On January 26, 2017, the FASB issued ASU 2017-04, “Intangibles—Goodwill and Other (Topic 350): Simplifying the Accounting for Goodwill Impairment.”

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2019
Acquisitions	D. ACQUISITIONS Lemsys SA On January 30, 2019, Teradyne acquired all of the issued and outstanding shares of Lemsys SA (“Lemsys”) for a total purchase price of approximately $9.1 million. Lemsys strengthens Teradyne’s position in the electrification trends of vehicles, solar, wind, and industrial applications. The Lemsys acquisition was accounted for as a business combination and, accordingly, the results have been included in Teradyne’s Semiconductor Test segment from the date of acquisition. As of the acquisition date, Teradyne’s preliminary purchase price allocation was goodwill of $1.2 million, which is not deductible for tax purposes, acquired intangible assets of $5.5 million with an average estimated useful life of 4.9 years, and $2.4 million of net tangible assets. The acquisition was not material to Teradyne’s condensed consolidated financial statements. Mobile Industrial Robots On April 25, 2018, The total purchase price of $197.8 million included $145.2 million of cash paid and $52.6 million of contingent consideration measured at fair value. The contingent consideration is payable in Euros upon the achievement of certain thresholds and targets for revenue and earnings before interest and taxes for periods from January 1, 2018 to December 31, 2018; January 1, 2018 to December 31, 2019; and January 1, 2018 to December 31, 2020. The contingent consideration related to revenue for the period from January 1, 2018 to December 31, 2018 in the amount of $30.8 million was paid in March 2019. The remaining maximum contingent consideration that could be paid is $83.2 million. The valuation of the contingent consideration is dependent on the following assumptions: forecasted revenues, revenue volatility, earnings before interest and taxes, and discount rate. These assumptions were estimated based on a review of the historical and projected results. The MiR acquisition was accounted for as a business combination and, accordingly, the results have been included in Teradyne’s consolidated results of operations from the date of acquisition. MiR’s products will help expand the Industrial Automation segment, which is a key component . The allocation of the total purchase price to MiR’s net tangible liabilities and identifiable intangible assets was based on their estimated fair values as of the acquisition date. The excess of the purchase price over the identifiable intangible assets and net tangible liabilities in the amount of $136.0 million was allocated to goodwill, which is not deductible for tax purposes. MiR’s results have been included in Teradyne’s Industrial Automation segment from the date of acquisition. The following table represents the final allocation of the purchase price: Purchase Price Allocation (in thousands) Goodwill $ 135,976 Intangible assets 80,670 Tangible assets acquired and liabilities assumed: Current assets 6,039 Non-current assets 1,336 Accounts payable and current liabilities (7,336 ) Long-term deferred tax liabilities (18,007 ) Other long-term liabilities (900 ) Total purchase price $ 197,778 Teradyne estimated the fair value of intangible assets using the income and cost approaches. Acquired intangible assets are amortized on a straight-line basis over their estimated useful lives. Components of these intangible assets and their estimated useful lives at the acquisition date are as follows: Fair Value Estimated Useful Life (in thousands) (in years) Developed technology $ 58,900 7.0 Trademarks and tradenames 13,240 11.0 Customer relationships 8,500 2.5 Backlog 30 0.2 Total intangible assets $ 80,670 7.2 The following unaudited pro forma information gives effect to the acquisition of MiR as if the acquisition occurred on January 1, 2017. The unaudited pro forma results are not necessarily indicative of what actually would have occurred had the acquisition been in effect for the periods presented: For the Three Months Ended April 1, 2018 (in thousands) Revenue $ 493,017 Net income 85,151 Net income per common share: Basic $ 0.44 Diluted $ 0.42 Pro forma results for the three months ended April 1, 2018 were adjusted to exclude $0.6 million of acquisition related costs. Energid Technologies Corporation On February 26, 2018, acquired all of the issued and outstanding shares of Energid for a total purchase price of approximately $27.6 million. Energid’s technology enables and simplifies the programming of complex robotic motions used in a wide variety of end markets, ranging from heavy industry to healthcare, utilizing both traditional robots and collaborative robots. The Energid acquisition was accounted for as a business combination and, accordingly, Energid’s results have been included in ’s Industrial Automation segment from the date of acquisition. As of the acquisition date, ’s purchase price allocation was goodwill of $14.4 million which is deductible for tax purposes, acquired intangible assets of $12.3 million with an average estimated useful life of 7.7 years, and $1.0 million of net tangible assets. The acquisition was not material to ’s condensed consolidated financial statements.

Revenue

Revenue	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	E. REVENUE Revenue recognized in accordance with ASC 606: “ Revenue from Contracts with Customers” For the three months ended March 31, 2019 and April 1, 2018, Teradyne also recognized $1.7 million and $4.3 million, respectively, of revenues from leases of Teradyne systems, which are accounted for outside of Disaggregation of Revenue The following table provides information about disaggregated revenue by primary geographical market, major product line and timing of revenue recognition. For the Three Months Ended March 31, 2019 Semiconductor Test System Test Industrial Automation Wireless Corporate Other Consolidated System on a Chip Memory Defense/ Aerospace Storage Production Universal Mobile Energid (in thousands) Americas Point in time $ 7,977 $ 8,051 $ 14,783 $ 1,593 $ 3,254 $ 15,297 $ 3,539 $ — $ 2,090 $ (151 ) $ 56,433 Over time 8,190 712 6,450 — 729 246 — 260 151 — 16,738 Europe, Middle East and Africa Point in time 11,032 153 39 — 5,064 25,904 3,840 — 736 — 46,768 Over time 5,281 280 469 — 1,554 416 — 289 45 — 8,334 Asia Pacific Point in time 219,746 35,571 263 16,605 3,636 14,178 1,727 — 24,628 — 316,354 Over time 38,913 3,280 764 2,054 920 228 — 212 1,359 — 47,730 Lease Revenue 1,667 — — — 43 — — — 32 — 1,742 Total $ 292,806 $ 48,047 $ 22,768 $ 20,252 $ 15,200 $ 56,269 $ 9,106 $ 761 $ 29,041 $ (151 ) $ 494,099 For the Three Months Ended April 1, 2018 Semiconductor Test System Test Industrial Automation Wireless Corporate Other Consolidated System on a Chip Memory Defense/ Aerospace Storage Production Universal Mobile Energid (in thousands) Americas Point in time $ 9,600 $ 2,862 $ 11,597 $ 279 $ 1,760 $ 14,373 $ — $ — $ 4,979 $ (221 ) $ 45,229 Over time 8,791 696 6,188 — 757 89 — — 112 — 16,633 Europe, Middle East and Africa Point in time 12,125 139 1,497 — 4,037 22,573 — — 1,041 — 41,412 Over time 5,214 269 551 — 1,559 143 — — 227 — 7,963 Asia Pacific Point in time 224,851 66,273 101 10,122 1,861 11,583 — — 13,664 — 328,455 Over time 36,338 2,323 208 1,533 735 73 — — 2,296 — 43,506 Lease Revenue 3,847 — — — 234 — — — 188 — 4,269 Total $ 300,766 $ 72,562 $ 20,142 $ 11,934 $ 10,943 $ 48,834 $ — $ — $ 22,507 $ (221 ) $ 487,467 Contract Balances The amount of revenue recognized during the three months ended March 31, 2019 and April 1, 2018 that was previously included within the deferred revenue and customer advances balance was $19.5 million and $21.8 million, respectively, and primarily relates to extended warranties, training, application support and post contract support. Each of these represents a distinct performance obligation. Teradyne expects to recognize 72% of the remaining performance obligation in the next 12 months, 22% in 1-3 years, and the remainder thereafter. Accounts Receivable Teradyne sells certain trade accounts receivables on a non-recourse basis to third-party financial institutions pursuant to factoring agreements. Teradyne accounts for these transactions as sales of receivables and presents cash proceeds as a cash provided by operating activities in the consolidated statements of cash flows. Total trade accounts receivable sold under the factoring agreements were $41.7 million and $3.5 million for the three months ended March 31, 2019 and April 1, 2018, respectively. Factoring fees for the sales of receivables were recorded in interest expense and were not material.

Inventories

Inventories	3 Months Ended
	Mar. 31, 2019
Inventories	F. INVENTORIES Inventories, net consisted of the following at March 31, 2019 and December 31, 2018: March 31, December 31, 2019 2018 (in thousands) Raw material $ 94,862 $ 89,365 Work-in-process 29,725 31,014 Finished goods 36,755 33,162 $ 161,342 $ 153,541 Inventory reserves at March 31, 2019 and December 31, 2018 were $100.9 million and $100.8 million, respectively.

Financial Instruments

Financial Instruments	3 Months Ended
	Mar. 31, 2019
Financial Instruments	G. FINANCIAL INSTRUMENTS Cash Equivalents Teradyne considers all highly liquid investments with maturities of three months or less at the date of acquisition to be cash equivalents. Marketable Securities Teradyne’s available-for-sale debt securities are classified as Level 2 and equity securities are classified as Level 1. Contingent consideration is classified as Level 3. The vast majority of Level 2 securities are fixed income securities priced by third party pricing vendors. These pricing vendors utilize the most recent observable market information in pricing these securities or, if specific prices are not available, use other observable inputs like market transactions involving identical or comparable securities. During the three months ended March 31, 2019 and April 1, 2018, there were no transfers in or out of Level 1, Level 2, or Level 3 financial instruments. Realized gains recorded in the three months ended March 31, 2019 and April 1, 2018 were $0.1 million and $0.3 million, respectively. Realized losses recorded in the three months ended March 31, 2019 and April 1, 2018 were $0.1 million and $1.5 million, respectively. Realized gains are included in interest income and realized losses are included in interest expense. Unrealized gains and losses on available-for-sale debt securities are included in accumulated other comprehensive income (loss) on the balance sheet. Unrealized gains on equity securities are included in interest income and unrealized losses are included in interest expense. Unrealized gains related to equity securities recognized in the three months ended March 31, 2019 were $2.8 million. The cost of securities sold is based on the specific identification method. The following table sets forth by fair value hierarchy Teradyne’s financial assets and liabilities that were measured at fair value on a recurring basis as of March 31, 2019 and December 31, 2018. March 31, 2019 Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in thousands) Assets Cash $ 222,714 $ — $ — $ 222,714 Cash equivalents 186,520 74,494 — 261,014 Available-for-sale securities: U.S. Treasury securities — 191,043 — 191,043 Commercial paper — 180,604 — 180,604 Corporate debt securities — 91,244 — 91,244 Certificates of deposit and time deposits — 11,496 — 11,496 U.S. government agency securities — 9,629 — 9,629 Debt mutual funds 3,331 — — 3,331 Non-U.S. government securities — 378 — 378 Equity securities: Mutual funds 25,289 — — 25,289 $ 437,854 $ 558,888 $ — $ 996,742 Derivative assets — 17 — 17 Total $ 437,854 $ 558,905 $ — $ 996,759 Liabilities Contingent consideration $ — $ — $ 38,313 $ 38,313 Derivative liabilities — 291 — 291 Total $ — $ 291 $ 38,313 $ 38,604 Reported as follows: (Level 1) (Level 2) (Level 3) Total (in thousands) Assets Cash and cash equivalents $ 409,234 $ 74,494 $ — $ 483,728 Marketable securities — 421,088 — 421,088 Long-term marketable securities 28,620 63,306 — 91,926 Prepayments — 17 — 17 Total $ 437,854 $ 558,905 $ — $ 996,759 Liabilities Other current liabilities $ — $ 291 $ — $ 291 Contingent consideration — — 22,803 22,803 Long-term contingent consideration — — 15,510 15,510 Total $ — $ 291 $ 38,313 $ 38,604 December 31, 2018 Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in thousands) Assets Cash $ 312,512 $ — $ — $ 312,512 Cash equivalents 253,525 360,715 — 614,240 Available-for-sale securities: U.S. Treasury securities — 109,721 — 109,721 Commercial paper — 86,117 — 86,117 Corporate debt securities — 40,020 — 40,020 U.S. government agency securities — 9,611 — 9,611 Certificates of deposit and time deposits — 7,604 — 7,604 Debt mutual funds 3,187 — — 3,187 Non-U.S. government securities — 376 — 376 Equity securities: Mutual funds 21,191 — — 21,191 $ 590,415 $ 614,164 $ — $ 1,204,579 Derivative assets — 79 — 79 Total $ 590,415 $ 614,243 $ — $ 1,204,658 Liabilities Contingent consideration $ — $ — $ 70,543 $ 70,543 Derivative liabilities — 514 — 514 Total $ — $ 514 $ 70,543 $ 71,057 Reported as follows: (Level 1) (Level 2) (Level 3) Total (in thousands) Assets Cash and cash equivalents $ 566,037 $ 360,715 $ — $ 926,752 Marketable securities — 190,096 — 190,096 Long-term marketable securities 24,378 63,353 — 87,731 Prepayments — 79 — 79 Total $ 590,415 $ 614,243 $ — $ 1,204,658 Liabilities Other accrued liabilities $ — $ 514 $ — $ 514 Contingent consideration — — 34,865 34,865 Long-term contingent consideration — — 35,678 35,678 Total $ — $ 514 $ 70,543 $ 71,057 Changes in the fair value of Level 3 contingent consideration for the three months ended March 31, 2019 and April 1, 2018 were as follows: For the Three Months Ended March 31, April 1, 2019 2018 (in thousands) Balance at beginning of period $ 70,543 $ 45,102 Foreign currency impact (610 ) — Payments (a) (34,590 ) (24,553 ) Fair value adjustment (b) 2,970 (4,968 ) Balance at end of period $ 38,313 $ 15,581 (a) In the three months ended March 31, 2019, Teradyne paid $ 30.8 $ 24.6 (b) In the three months ended March 31, 2019, the fair value of contingent consideration for the earn-out in connection with the acquisition of MiR was increased by $ 3.0 $ 5.0 The following table provides quantitative information associated with the fair value measurement of Teradyne’s Level 3 financial instruments: Liability March 31, 2019 Fair Value Valuation Technique Unobservable Inputs Weighted Average (in thousands) Contingent consideration (MiR) $ 38,313 Monte Carlo Simulation Revenue volatility 17.0 % Discount Rate 0.4 % As of March 31, 2019, the significant unobservable inputs used in the Monte Carlo simulation to fair value the MiR contingent consideration include forecasted revenues, revenue volatility, earnings before interest and taxes, and discount rate. Increases or decreases in the inputs would result in a higher or lower fair value measurement. As of March 31, 2019, the maximum amount of contingent consideration that could be paid in connection with the acquisition of MiR is $83.2 million. December 31, 2019 and December 31, 2020. The carrying amounts and fair values of Teradyne’s financial instruments at March 31, 2019 and December 31, 2018 were as follows: March 31, 2019 December 31, 2018 Carrying Value Fair Value Carrying Value Fair Value (in thousands) Assets Cash and cash equivalents $ 483,728 $ 483,728 $ 926,752 $ 926,752 Marketable securities 513,014 513,014 277,827 277,827 Derivative assets 17 17 79 79 Liabilities Contingent consideration 38,313 38,313 70,543 70,543 Derivative liabilities 291 291 514 514 Convertible debt (1) 383,590 644,575 379,981 547,113 (1) The carrying value represents the bifurcated debt component only, while the fair value is based on quoted market prices for the convertible note, which includes the equity conversion features. The fair values of accounts receivable, net and accounts payable approximate the carrying value due to the short-term nature of these instruments. The following table summarizes the composition of available-for-sale marketable securities at March 31, 2019: March 31, 2019 Available-for-Sale Cost Unrealized Gain Unrealized (Loss) Fair Market Value Fair Market Value of Investments with Unrealized Losses (in thousands) U.S. Treasury securities $ 191,715 $ 144 $ (816 ) $ 191,043 $ 82,132 Commercial paper 180,610 1 (7 ) 180,604 11,237 Corporate debt securities 90,402 1,343 (501 ) 91,244 18,150 Certificates of deposit and time deposits 11,497 1 (2 ) 11,496 4,419 U.S. government agency securities 9,646 4 (21 ) 9,629 4,101 Debt mutual funds 3,255 76 — 3,331 — Non-U.S. government securities 378 — — 378 — $ 487,503 $ 1,569 $ (1,347 ) $ 487,725 $ 120,039 Reported as follows: Cost Unrealized Gain Unrealized (Loss) Fair Market Value Fair Market Value of Investments with Unrealized Losses (in thousands) Marketable securities $ 421,024 $ 126 $ (62 ) $ 421,088 $ 91,100 Long-term marketable securities 66,479 1,443 (1,285 ) 66,637 28,939 $ 487,503 $ 1,569 $ (1,347 ) $ 487,725 $ 120,039 The following table summarizes the composition of available-for-sale marketable securities at December 31, 2018: December 31, 2018 Available-for-Sale Cost Unrealized Gain Unrealized (Loss) Fair Value Market Fair Market Value of Investments with Unrealized Losses (in thousands) U.S. Treasury securities $ 110,969 $ 112 $ (1,360 ) $ 109,721 $ 75,040 Commercial paper 86,130 13 (26 ) 86,117 85,094 Corporate debt securities 41,133 432 (1,545 ) 40,020 24,767 U.S. government agency securities 9,646 1 (36 ) 9,611 7,077 Certificates of deposit and time deposits 7,604 — — 7,604 — Debt mutual funds 3,153 34 — 3,187 — Non-U.S. government securities 376 — — 376 — $ 259,011 $ 592 $ (2,967 ) $ 256,636 $ 191,978 Reported as follows: Cost Unrealized Gain Unrealized (Loss) Fair Value Market Fair Market Value of Investments with Unrealized Losses (in thousands) Marketable securities $ 190,100 $ 88 $ (92 ) $ 190,096 $ 140,262 Long-term marketable securities 68,911 504 (2,875 ) 66,540 51,716 $ 259,011 $ 592 $ (2,967 ) $ 256,636 $ 191,978 As of March 31, 2019, the fair market value of investments in available-for-sale securities with unrealized losses totaled $120.0 million. Of this value, $32.9 million had unrealized losses of $1.3 million for greater than one year and $87.1 million had unrealized losses of $0.1 million for less than one year. As of December 31, 2018, the fair market value of investments with unrealized losses totaled $192.0 million. Of this value, $28.5 million had unrealized losses of $1.6 million greater than one year and $163.5 million had unrealized losses of $1.4 million for less than one year. Teradyne reviews its investments to identify and evaluate investments that have an indication of possible impairment. Based on this review, Teradyne determined that the unrealized losses related to these investments at March 31, 2019 and December 31, 2018 were temporary. The contractual maturities of investments in available-for-sale securities held at March 31, 2019 were as follows: March 31, 2019 Cost Fair Market Value (in thousands) Due within one year $ 421,024 $ 421,088 Due after 1 year through 5 years 9,325 9,343 Due after 5 years through 10 years 14,026 13,659 Due after 10 years 39,873 40,304 Total $ 484,248 $ 484,394 Contractual maturities of investments in available-for-sale securities held at March 31, 2019 exclude $3.3 million of debt mutual funds as they do not have a contractual maturity date. Derivatives Teradyne conducts business in a number of foreign countries, with certain transactions denominated in local currencies. The purpose of Teradyne’s foreign currency management is to minimize the effect of exchange rate fluctuations on certain foreign currency denominated monetary assets and liabilities. Teradyne does not use derivative financial instruments for trading or speculative purposes. To minimize the effect of exchange rate fluctuations associated with the remeasurement of monetary assets and liabilities denominated in foreign currencies, Teradyne enters into foreign currency forward contracts. The change in fair value of these derivatives is recorded directly in earnings, and is used to offset the change in value of monetary assets and liabilities denominated in foreign currencies. The notional amount of foreign currency forward contracts at March 31, 2019 and December 31, 2018 was $148.8 million and $163.1 million, respectively. Gains and losses on foreign currency forward contracts and foreign currency remeasurement gains and losses on monetary assets and liabilities are included in other (income) expense, net. The following table summarizes the fair value of derivative instruments as of March 31, 2019 and December 31, 2018: Balance Sheet Location March 31, December 31, (in thousands) Derivatives not designated as hedging instruments: Foreign exchange contracts Prepayments $ 17 $ 79 Foreign exchange contracts Other current liabilities (291 ) (514 ) Total derivatives $ (274 ) $ (435 ) The following table summarizes the effect of derivative instruments recognized in the statement of operations for the three months ended March 31, 2019 and April 1, 2018. Location of Losses (Gains) For the Three Months Ended Recognized in March 31, April 1, Statement of Operations 2019 2018 (in thousands) Derivatives not designated as hedging instruments: Foreign exchange contracts Other (income) expense, net $ 3,934 $ 1,575 (1) The table does not reflect the corresponding gains and losses from the remeasurement of monetary assets and liabilities denominated in foreign currencies. (2) For the three months ended March 31, 2019 and April 1, 2018, net gains from the remeasurement of monetary assets and liabilities denominated in foreign currencies were $ 3.2 0.6 See Note I: “Debt” regarding derivatives related to the convertible senior notes.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Lease	H. LEASES On January 1, 2019, Teradyne adopted ASC 842 using the modified retrospective approach. Under this method of adoption, the comparative information in the consolidated financial statements has not been revised and continues to be reported under the previously applicable lease accounting guidance (ASC 840). Adoption of ASC 842 resulted in recording ROU assets and lease liabilities of approximately $50.1 million and $54.3 million, respectively. The adoption of ASC 842 did not have a material impact on beginning retained earnings, the consolidated statement of operations, cash flows, or earnings per share. Teradyne has facility and auto leases, which are accounted for as operating leases. Teradyne’s facility leases are primarily used for administrative functions, research and development, manufacturing, and storage and distribution. Remaining lease terms range from less than one year to ten years. Total lease expense for the three months ended March 31, 2019 was $7.2 million, and included $1.4 million of variable lease costs and $0.7 million of costs related to short terms leases which are not recorded on the consolidated balance sheets. At March 31, 2019, the weighted average remaining lease term and weighted average discount rate for operating leases was 4.2 years and 5.1%, respectively. Supplemental cash flow information related to leases was as follows: For the Three Months March 31, (in thousands) Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows $ 5,059 Right-of-use assets obtained in exchange for new lease obligations 5,737 Maturities of lease liabilities as of March 31, 2019 were as follows: Operating Leases (in thousands) 2019 $ 15,375 2020 18,967 2021 14,514 2022 10,262 2023 5,719 Thereafter 11,484 Total lease payments 76,321 Less imputed interest (21,083 ) Total lease liabilities $ 55,238 As of December 31, 2018, future non-cancelable rent obligations as determined under ASC 840 were as follows: Operating Leases (in thousands) 2019 $ 19,570 2020 18,293 2021 13,578 2022 9,693 2023 5,449 Thereafter 9,472 Total lease payments $ 76,055

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Debt	I. DEBT Convertible Senior Notes On December 12, 2016, Teradyne completed a private offering of $460.0 million aggregate principal amount of 1.25% convertible senior unsecured notes (the “Notes”) due December 15, 2023 and received net proceeds, after issuance costs, of approximately $450.8 million, $33.0 million of which was used to pay the net cost of the convertible note hedge transactions and $50.1 million of which was used to repurchase 2.0 million shares of Teradyne’s common stock under its existing stock repurchase program from purchasers of the Notes in privately negotiated transactions effected through one of the initial purchasers or its affiliates conducted concurrently with the pricing of the Note offering. The Notes will mature on December 15, 2023, unless earlier repurchased or converted. The Notes bear interest from December 12, 2016 at a rate of 1.25% per year payable semiannually in arrears on June 15 and December 15 of each year Concurrent with the offering of the Notes, Teradyne entered into convertible note hedge transactions (the “Note Hedge Transactions”) with the initial purchasers or their affiliates (the “Option Counterparties”). The Note Hedge Transactions cover, subject to customary anti-dilution adjustments, the number of shares of the common stock that underlie the Notes, with a strike price equal to the conversion price of the Notes of $31.70. The Note Hedge Transactions cover, subject to customary anti-dilution adjustments, approximately 14.5 million shares of Teradyne’s common stock. Separately and concurrent with the pricing of the Notes, Teradyne entered into warrant transactions with the Option Counterparties (the “Warrant Transactions”) in which it sold net-share-settled (or, at its election subject to certain conditions, cash-settled) warrants to the Option Counterparties. The Warrant Transactions cover, subject to customary anti-dilution adjustments, approximately 14.5 million shares of common stock. As of March 31, 2019, the strike price of the warrants was approximately $39.78 per share. The strike price is subject to adjustment under certain circumstances. The Warrant Transactions could have a dilutive effect to Teradyne’s common stock to the extent that the market price per share of Teradyne’s common stock, as measured under the terms of the Warrant Transactions, exceeds the applicable strike price of the warrants. The Note Hedge Transactions are expected to reduce the potential dilution to Teradyne’s common stock upon any conversion of the Notes. However, the Warrant Transactions could separately have a dilutive effect to the extent that the market value per share of Teradyne’s common stock exceeds the applicable strike price of the warrant. The net cost of the Note Hedge Transactions, after being partially offset by the proceeds from the sale of the warrants, was approximately $33.0 million. In connection with establishing their initial hedge of these convertible note hedge and warrant transactions, the Option Counterparties have entered into various derivative transactions with respect to Teradyne’s common stock and/or purchased shares of Teradyne’s common stock or other securities, including the Notes, concurrent with, or shortly after, the pricing of the Notes. In addition, the Option Counterparties may modify their hedge positions by entering into or unwinding various derivative transactions with respect to Teradyne’s common stock or by selling Teradyne’s common stock or other securities, including the Notes, in secondary market transactions (and may do so during any observation period related to the conversion of the Notes). These activities could adversely affect the value of Teradyne’s common stock and the Notes. Teradyne considered “Derivatives and Hedging—Contracts in Entity’s Own Equity,” Teradyne assessed whether the convertible note hedge should be classified as equity under ASC 815-40. In the Note Hedge Transactions contract the settlement terms permit net cash settlement or net share settlement, at the option of Teradyne. Therefore, the criteria as set forth in ASC 815-40 were evaluated by Teradyne. In reviewing the criteria, Teradyne noted the following: (1) the convertible note hedge does not require Teradyne to issue shares; (2) there is no requirement to net cash settle the convertible note hedge for failure to make timely filings with the SEC; (3) in the case of termination, the convertible note hedge is settled in the same consideration as the holders of the underlying stock; (4) the counterparty does not have rights that rank higher than those of a shareholder of the stock underlying the convertible note hedge; and (5) there is no requirement to post collateral. Based on its analysis of those criteria, Teradyne concluded that the convertible note hedge should be recorded in equity and no further adjustment should be made in future periods to adjust the value of the convertible note hedge. Teradyne analyzed the Warrant Transactions under ASC 815-40, “Derivatives and Hedging—Contracts in Entity’s Own Equity,” The provisions of ASC 470-20, “ Debt with Conversion and Other Options, The below tables represent the key components of Teradyne’s convertible senior notes: March 31, 2019 December 31, 2018 (in thousands) Debt Principal $ 460,000 $ 460,000 Unamortized discount 76,410 80,019 Net Carrying amount of convertible debt $ 383,590 $ 379,981 For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Contractual interest expense on the coupon $ 1,438 $ 1,438 Amortization of the discount component recognized as interest expense 3,608 3,434 Total interest expense on the convertible debt $ 5,046 $ 4,872 As of March 31, 2019, the remaining unamortized discount was $76.4 million, which will be amortized over 4.7 years using the effective interest rate method. The carrying amount of the equity component was $100.8 million. As of March 31, 2019, the if-converted value of the Notes was $578.1 million. Revolving Credit Facility On April 27, 2015, Teradyne entered into a Credit Agreement (the “Credit Agreement”) with Barclays Bank PLC, as administrative agent and collateral agent, and the lenders party thereto. The Credit Agreement provides for a five-year, senior secured revolving credit facility of up to $350 million (the “Credit Facility”). The Credit Agreement further provides that, subject to customary conditions, Teradyne may seek to obtain from existing or new lenders incremental commitments under the Credit Facility in an aggregate principal amount not to exceed $150 million. Proceeds from the Credit Facility may be used for general corporate purposes and working capital. Teradyne incurred $2.3 million in costs related to the revolving credit facility. These costs are being amortized over the five-year term of the revolving credit facility and are included in interest expense in the statements of operations. As of May 10, 2019, Teradyne has not borrowed any funds under the Credit Facility. The interest rates applicable to loans under the Credit Facility are, at Teradyne’s option, equal to either a base rate plus a margin ranging from 0.00% to 1.00% per annum or LIBOR plus a margin ranging from 1.00% to 2.00% per annum, based on the Consolidated Leverage Ratio of Teradyne and its Restricted Subsidiaries. In addition, Teradyne will pay a commitment fee on the unused portion of the commitments under the Credit Facility ranging from 0.125% to 0.350% per annum, based on the then applicable Consolidated Leverage Ratio. Teradyne is not required to repay any loans under the Credit Facility prior to maturity, subject to certain customary exceptions. Teradyne is permitted to prepay all or any portion of the loans under the Credit Facility prior to maturity without premium or penalty, other than customary LIBOR breakage costs. The Credit Agreement contains customary events of default, representations, warranties and affirmative and negative covenants that, among other things, limit Teradyne’s and its Restricted Subsidiaries’ ability to sell assets, grant liens on assets, incur other secured indebtedness and make certain investments and restricted payments, all subject to exceptions set forth in the Credit Agreement. The Credit Agreement also requires Teradyne to satisfy two financial ratios measured as of the end of each fiscal quarter: a consolidated leverage ratio and an interest coverage ratio. As of May 10, 2019, Teradyne was in compliance with all covenants. The Credit Facility is guaranteed by certain of ’s domestic subsidiaries and by assets of and such subsidiaries, including a pledge of 65% of the capital stock of certain foreign subsidiaries.

Prepayments

Prepayments	3 Months Ended
	Mar. 31, 2019
Prepayments	J. PREPAYMENTS Prepayments consist of the following and are included in prepayments and other assets on the balance sheet: March 31, December 31, 2019 2018 (in thousands) Contract manufacturer and supplier prepayments $ 147,015 $ 131,642 Prepaid taxes 13,404 9,646 Prepaid maintenance and other services 7,703 8,487 Other prepayments 16,111 12,744 Total prepayments $ 184,233 $ 162,519

Deferred Revenue and Customer A

Deferred Revenue and Customer Advances	3 Months Ended
	Mar. 31, 2019
Deferred Revenue and Customer Advances	K. DEFERRED REVENUE AND CUSTOMER ADVANCES Deferred revenue and customer advances consist of the following and are included in short and long-term deferred revenue and customer advances on the balance sheet: March 31, December 31, 2019 2018 (in thousands) Maintenance and training $ 58,394 $ 58,362 Extended warranty 27,242 27,422 Customer advances, undelivered performance obligations and other 31,971 24,677 Total deferred revenue and customer advances $ 117,607 $ 110,461

Product Warranty

Product Warranty	3 Months Ended
	Mar. 31, 2019
Product Warranty	L. PRODUCT WARRANTY Teradyne generally provides a one-year warranty on its products, commencing upon installation, acceptance, delivery or shipment. A provision is recorded upon revenue recognition to cost of revenues for estimated warranty expense based on historical experience. Related costs are charged to the warranty accrual as incurred. The warranty balance below is included in other accrued liabilities on the balance sheet. For the Three Months Ended March 31, April 1, 2019 2018 (in thousands) Balance at beginning of period $ 7,909 $ 8,200 Acquisition 14 — Accruals for warranties issued during the period 3,066 3,063 Accruals related to pre-existing warranties 1,330 (139 ) Settlements made during the period (4,567 ) (3,576 ) Balance at end of period $ 7,752 $ 7,548 When Teradyne receives revenue for extended warranties, beyond one year, it is deferred and recognized on a straight-line basis over the contract period. Related costs are expensed as incurred. The balance below is included in short and long-term deferred revenue and customer advances on the balance sheet. For the Three Months Ended March 31, April 1, 2019 2018 (in thousands) Balance at beginning of period $ 27,422 $ 24,438 Deferral of new extended warranty revenue 5,820 5,139 Recognition of extended warranty deferred revenue (6,000 ) (4,987 ) Balance at end of period $ 27,242 $ 24,590

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2019
Stock-Based Compensation	M. STOCK-BASED COMPENSATION Under Teradyne’s stock compensation plans, Teradyne grants stock options, restricted stock units and performance-based restricted stock units, and employees are eligible to purchase Teradyne’s common stock through its Employee Stock Purchase Plan (“ESPP”). Time-based restricted stock unit awards granted to employees vest in equal annual installments over four years. Restricted stock unit awards granted to non-employee directors vest after a one Teradyne grants performance-based restricted stock units (“PRSUs”) to its executive officers with a performance metric based on relative total shareholder return (“TSR”). Teradyne’s three-year TSR performance is measured against the New York Stock Exchange (“NYSE”) Composite Index. The final number of TSR PRSUs that vest will vary based upon the level of performance achieved from 200% to 0% of the target shares capped at four times the grant date value. The TSR PRSUs will vest upon the three-year anniversary of the grant date. The TSR PRSUs are valued using a Monte Carlo simulation model. The number of units expected to be earned, based upon the achievement of the TSR market condition, is factored into the grant date Monte Carlo valuation. Compensation expense is recognized on a straight-line basis over the shorter of the three-year service period or the period from the grant to the date described in the retirement provisions below. Compensation expense for employees meeting the retirement provisions prior to the grant date will be recognized in full on the date of the grant. Compensation expense is recognized regardless of the eventual number of units that are earned based upon the market condition, provided the executive officer remains an employee at the end of the three-year period. Compensation expense is reversed if at any time during the three-year service period the executive officer is no longer an employee, subject to the retirement and termination eligibility provisions noted below. In January 2019 and 2018, Teradyne granted PRSUs to its executive officers with a performance metric based on three-year cumulative non-GAAP profit before interest and tax (“PBIT”) as a percent of Teradyne’s revenue. Non-GAAP PBIT is a financial measure equal to GAAP income from operations less restructuring and other, net; amortization of acquired intangible assets; acquisition and divestiture related charges or credits; pension actuarial gains and losses; non-cash convertible debt interest expense; and other non-recurring gains and charges. The final number of PBIT PRSUs that vest will vary based upon the level of performance achieved from 200% to 0% of the target shares. The PBIT PRSUs will vest upon the three-year anniversary of the grant date. Compensation expense is recognized on a straight-line basis over the shorter of the three year service period or the period from the grant date to the date described in the retirement provisions below. Compensation expense for employees meeting the retirement provisions prior to the grant date will be recognized in full on the date of grant. Compensation expense is recognized based on the number of units that are earned based upon the three-year Teradyne PBIT as a percent of Teradyne’s revenue, provided the executive officer remains an employee at the end of the three-year period subject to the retirement and termination eligibility provisions noted below. If a PRSU recipient’s employment ends prior to the determination of the performance percentage due to (1) permanent disability or death or (2) retirement or termination other than for cause, after attaining both at least age sixty and at least ten years of service, then all or a portion of the recipient’s PRSUs (based on the actual performance percentage achieved on the determination date) will vest on the date the performance percentage is determined. Except as set forth in the preceding sentence, no PRSUs will vest if the executive officer is no longer an employee at the end of the three-year period. During the three months ended March 31, 2019 and April 1, 2018, Teradyne granted 0.1 million and 0.1 million TSR PRSUs, respectively, with a grant date fair value of $48.47 and $54.85, respectively. The fair value was estimated using the Monte Carlo simulation model with the following assumptions: For the Three Months Ended March 31, April 1, 2019 2018 Risk-free interest rate 2.6 % 2.2 % Teradyne volatility-historical 31.8 % 26.8 % NYSE Composite Index volatility-historical 12.0 % 12.4 % Dividend yield 1.0 % 0.8 % Expected volatility was based on the historical volatility of Teradyne’s stock and the NYSE Composite Index for the 2019 and 2018 grant over the most recent three-year period. The risk-free interest rate was determined using the U.S. Treasury yield curve in effect at the time of grant. Dividend yield was based upon an estimated annual dividend amount of $0.36 per share for 2019 grants and 2018 grants, divided by Teradyne’s stock price on the grant date of $36.75 for the 2019 grant and $47.70 for the 2018 grant. During the three months ended March 31, 2019 and April 1, 2018, Teradyne granted 0.1 million and 0.1 million, respectively, of PBIT PRSUs with a grant date fair value of $35.67 and $46.62, respectively. During the three months ended March 31, 2019, Teradyne granted 0.6 million of service-based restricted stock unit awards to employees at a weighted average grant date fair value of $35.88 and 0.1 million of service-based stock options to executive officers at a weighted average grant date fair value of $10.26. During the three months ended April 1, 2018, Teradyne granted 0.5 million of service-based restricted stock unit awards to employees at a weighted average grant date fair value of $46.58 and 0.1 million of service-based stock options to executive officers at a weighted average grant date fair value of $12.17. Restricted stock unit awards granted to employees vest in equal annual installments over four seven The fair value of stock options was estimated using the Black-Scholes option-pricing model with the following assumptions: For the Three Months Ended March 31, April 1, 2019 2018 Expected life (years) 5.0 5.0 Risk-free interest rate 2.6 % 2.4 % Volatility-historical 30.1 % 26.4 % Dividend yield 1.0 % 0.8 % Teradyne determined the stock options’ expected life based upon historical exercise data for executive officers, the age of the executive officers and the terms of the stock option grant. Volatility was determined using historical volatility for a period equal to the expected life. The risk-free interest rate was determined using the U.S. Treasury yield curve in effect at the time of grant. Dividend yield was based upon an estimated annual dividend amount of $0.36 per share for 2019 and 2018 grants divided by Teradyne’s stock price on the grant date of $36.75 for the 2019 grant and $47.70 for the 2018 grant.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss)	N. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Changes in accumulated other comprehensive income (loss), which are presented net of tax, consist of the following: Foreign Currency Translation Adjustment Unrealized Gains (Losses) on Marketable Securities Retirement Plans Prior Service Credit Total (in thousands) Three Months Ended March 31, 2019 Balance at December 31, 2018, net of tax of $0, $(521), $(1,081), respectively $ (12,523 ) $ (1,845 ) $ 1,328 $ (13,040 ) Other comprehensive income before reclassifications, net of tax of $0, $577, $0, respectively (4,659 ) 2,100 — (2,559 ) Amounts reclassified from accumulated other comprehensive income, net of tax of $0, $(20), $(11), respectively — (70 ) (37 ) (107 ) Net current period other comprehensive income (loss), net of tax o f $0, $557, $(11), respectively (4,659 ) 2,030 (37 ) (2,666 ) Balance at March 31, 2019, net of tax of $0, $36, $(1,092), respectively $ (17,182 ) $ 185 $ 1,291 $ (15,706 ) Foreign Currency Translation Adjustments Unrealized Gains (Losses) on Marketable Securities Retirement Plans Prior Service Credit Total (in thousands) Three Months Ended April 1, 2018 Balance at December 31, 2017, net of tax of $0, $1,815, $(932), respectively $ 15,919 $ 1,362 $ 1,495 $ 18,776 Other comprehensive income (loss) before reclassifications, net of tax of $0, $(718), $0, respectively 10,541 (2,687 ) — 7,854 Amounts reclassified from accumulated other comprehensive income, net of tax of $0, $78, $(18), respectively — 1,668 (61 ) 1,607 Net current period other comprehensive income (loss), net of tax of $0, $(640), $(18), respectively 10,541 (1,019 ) (61 ) 9,461 Reclassification of income tax effects from the Tax Reform Act, net of tax of $0, $(691), $(78), respectively (a) — 691 78 769 Reclassification of unrealized gains on equity securities, net of tax of $0, $(902), $0, respectively (b) — (3,125 ) — (3,125 ) Balance as April 1, 2018, net of tax of $0, $(418), $(1,028), respectively $ 26,460 $ (2,091 ) $ 1,512 $ 25,881 (a) In the three months ended , Teradyne early adopted the ASU 2018-02, “Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” (b) 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 Reclassifications out of accumulated other comprehensive income (loss) to the statement of operations for the three months ended March 31, 2019 and April 1, 2018 were as follows: Details about Accumulated Other Comprehensive Income Components For the Three Months Ended Affected Line Item in the Statements of Operations March 31, April 1, 018 (in thousands) Available-for-sale marketable securities: Unrealized gains (losses), net of tax of $ 20 78 $ 70 $ (1,668 ) Interest (expense) income Defined benefit pension and postretirement plans: Amortization of prior service benefit, net of tax of $ 11 18 37 61 (a) Total reclassifications, net of tax of $ 31 60 $ 107 $ (1,607 ) Net income (a) The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit. See Note R: “Retirement Plans.”

Goodwill and Acquired Intangibl

Goodwill and Acquired Intangible Assets	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets	O. GOODWILL AND ACQUIRED INTANGIBLE ASSETS Goodwill Teradyne performs its annual goodwill impairment test as required under the provisions of ASC 350-10, “Intangibles—Goodwill and Other” The changes in the carrying amount of goodwill by reportable segments for the three months ended March 31, 2019, were as follows: Industrial Automation System Test Wireless Test Semiconductor Test Total (in thousands) Balance at December 31, 2018 Goodwill $ 363,358 $ 158,699 $ 361,819 $ 260,540 $ 1,144,416 Accumulated impairment losses — (148,183 ) (353,843 ) (260,540 ) (762,566 ) 363,358 10,516 7,976 — 381,850 Lemsys acquisition — — — 1,145 1,145 Foreign currency translation adjustment (3,494 ) — — 12 (3,482 ) Balance at March 31, 2019 Goodwill 359,864 158,699 361,819 261,697 1,142,079 Accumulated impairment losses — (148,183 ) (353,843 ) (260,540 ) (762,566 ) $ 359,864 $ 10,516 $ 7,976 $ 1,157 $ 379,513 Intangible Assets Teradyne reviews long-lived assets for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable or that the useful lives of these assets are no longer appropriate. Amortizable intangible assets consist of the following and are included in intangible assets, net on the balance sheet: March 31, 2019 Gross Carrying Amount (1) Accumulated Amortization Foreign Translation Adjustment Net Carrying Amount (in thousands) Developed technology $ 337,218 $ (259,129 ) $ (4,812 ) $ 73,277 Customer relationships 100,743 (85,469 ) (408 ) 14,866 Tradenames and trademarks 64,670 (32,897 ) (973 ) 30,800 Non-compete agreement 320 (320 ) — — Backlog 780 (349 ) (2 ) 429 Total intangible assets $ 503,731 $ (378,164 ) $ (6,195 ) $ 119,372 December 31, 2018 Gross Carrying Amount Accumulated Amortization Foreign Translation Adjustment Net Carrying Amount (in thousands) Developed technology $ 336,308 $ (252,080 ) $ (4,079 ) $ 80,149 Customer relationships 97,153 (83,448 ) (340 ) 13,365 Tradenames and trademarks 64,420 (31,653 ) (799 ) 31,968 Non-compete agreement 320 (320 ) — — Backlog 30 (30 ) — — Total intangible assets $ 498,231 $ (367,531 ) $ (5,218 ) $ 125,482 (1) Includes $5.5 million of intangible assets Aggregate intangible asset amortization expense was $10.6 million and $7.7 million, for the three months ended March 31, 2019 and April 1, 2018 Estimated intangible asset amortization expense for each of the five succeeding fiscal years is as follows: Year Amortization Expense (in thousands) 2019 (remainder) 29,184 2020 24,852 2021 14,707 2022 13,815 2023 13,339 Thereafter 23,475

Net Income Per Common Share

Net Income Per Common Share	3 Months Ended
	Mar. 31, 2019
Net Income (Loss) per Common Share	P. NET INCOME PER COMMON SHARE The following table sets forth the computation of basic and diluted net income per common share: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands, except per share amounts) Net income for basic and diluted net income per share $ 109,138 $ 86,974 Weighted average common shares-basic 173,532 195,255 Effect of dilutive potential common shares: Incremental shares from assumed conversion of convertible notes (1) 2,186 4,398 Convertible note hedge warrant shares (2) — 1,830 Restricted stock units 1,021 1,666 Stock options 222 321 Employee stock purchase plan 11 14 Dilutive potential common shares 3,440 8,229 Weighted average common shares-diluted 176,972 203,484 Net income per common share-basic $ 0.63 $ 0.45 Net income per common share-diluted $ 0.62 $ 0.43 (1) Incremental shares from assumed conversion of the convertible notes was calculated using the difference between the average Teradyne stock price for the period and the conversion price of $31.70, multiplied by 14.5 million shares. The result of this calculation, representing the total intrinsic value of the convertible debt, was divided by the average Teradyne stock price for the period. (2) Convertible notes hedge warrant shares were calculated using the difference between the average Teradyne stock price for the period and the warrant price of $39.78, multiplied by 14.5 million shares. The result of this calculation, representing the total intrinsic value of the warrant, was divided by the average Teradyne stock price for the period. The computation of diluted net income per common share for the three months ended March 31, 2019 excludes the effect of the potential vesting of 0.6 million of restricted stock units because the effect would have been anti-dilutive. The computation of diluted net income per common share for the three months ended April 1, 2018 excludes the effect of the potential vesting of 0.4 million shares of restricted stock units because the effect would have been anti-dilutive.

Restructuring and Other

Restructuring and Other	3 Months Ended
	Mar. 31, 2019
Restructuring and Other	Q. RESTRUCTURING AND OTHER During the three months ended March 31, 2019, $3.0 , $1.3 $0.8 . During the three months ended April 1, 2018, recorded a $5.0 million credit for the decrease in the fair value of the Universal Robots contingent consideration liability, partially offset by $3.9 million recorded for employee severance charges, primarily in Semiconductor Test, and $0.8 million of acquisition related expenses.

Retirement Plans

Retirement Plans	3 Months Ended
	Mar. 31, 2019
Retirement Plans	R. RETIREMENT PLANS ASC 715, “Compensation—Retirement Benefits” Defined Benefit Pension Plans Teradyne has defined benefit pension plans covering a portion of domestic employees and employees of certain non-U.S. subsidiaries. Benefits under these plans are based on employees’ years of service and compensation. Teradyne’s funding policy is to make contributions to these plans in accordance with local laws and to the extent that such contributions are tax deductible. The assets of the U.S. qualified pension plan consist primarily of fixed income and equity securities. In addition, Teradyne has unfunded qualified foreign plans as well as an unfunded supplemental executive defined benefit plan in the United States to provide retirement benefits in excess of levels allowed by the Employment Retirement Income Security Act (“ERISA”) and the Internal Revenue Code (“IRC”). In the three months ended March 31, 2019, Teradyne contributed $0.7 million to the U.S. supplemental executive defined benefit pension plan and $0.2 million to certain qualified pension plans for non-U.S. subsidiaries. For the three months ended March 31, 2019 and April 1, 2018, Teradyne’s net periodic pension cost was comprised of the following: For the Three Months Ended March 31, 2019 April 1, 2018 United States Foreign United States Foreign (in thousands) Service cost $ 405 $ 188 $ 571 $ 213 Interest cost 1,795 173 2,997 186 Expected return on plan assets (1,511 ) (7 ) (3,369 ) (5 ) Amortization of prior service cost — — 14 — Total net periodic pension cost $ 689 $ 354 $ 213 $ 394 Postretirement Benefit Plan In addition to receiving pension benefits, Teradyne employees in the United States who meet early retirement eligibility requirements as of their termination dates may participate in Teradyne’s Welfare Plan, which includes medical and dental benefits up to age 65. Death benefits provide a fixed sum to retirees’ survivors and are available to all retirees. Substantially all of Teradyne’s current U.S. employees could become eligible for these benefits, and the existing benefit obligation relates primarily to those employees. For the three months ended March 31, 2019 and April 1, 2018, Teradyne’s net periodic postretirement benefit cost was comprised of the following: For the Three March 31, April 1, 2018 (in thousands) Service cost $ 9 $ 9 Interest cost 85 50 Amortization of prior service credit (48 ) (93 ) Special termination benefits — 1,626 Total net periodic postretirement benefit cost $ 46 $ 1,592

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies	S. COMMITMENTS AND CONTINGENCIES Purchase Commitments As of March 31, 2019, Teradyne had entered into purchase commitments for certain components and materials. The purchase commitments covered by the agreements aggregate to approximately $263.0 million, of which $255.3 million is for less than one year. Legal Claims Teradyne is subject to various legal proceedings and claims which have arise n in the ordinary course of business. In the opinion of management, the ultimate disposition of these matters will not have a material adverse effect on ’s results of operations, financial condition or cash flows.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Taxes	T. INCOME TAXES The effective tax rate for the three months ended March 31, 2019 and April 1, 2018 was (16.1)% and 9.2%, respectively. The decrease in the effective tax rate from the three months ended April 1, 2018 to the three months ended March 31, 2019 resulted from The effective tax rate for the three months ended March 31, 2019 and April 1, 2018 was lower than the expected federal statutory rate because of the favorable effect of statutory rates applicable to income earned outside the United States, the benefit from U.S. research and development tax credits, the benefit from stock based compensation deductions, and the benefit of the U.S. foreign derived intangible income deduction partially offset by the U.S. global intangible low-taxed income inclusion. The effective tax rate for the three months ended March 31, 2019 was also reduced by discrete tax benefits from the release of reserves for uncertain tax positions. The effective rate for the three months ended April 1, 2018 was also increased by additions to the uncertain tax positions for transfer pricing. Discrete tax items recorded in the three months ended March 31, 2019 amounted to $30.2 million of net benefit. The $30.2 million of discrete tax benefit consisted of $ million of benefit resulting from the Discrete tax items recorded in the three months ended April 1, 2018 amounted to $6.0 million of net benefit. The $6.0 million of discrete tax benefit consisted of $7.6 million of benefit from stock based compensation, $1.7 million of expense from the write down of deferred tax assets as a result of reductions in tax rates, $0.7 million of other discrete tax benefits and $0.6 million of other discrete tax expenses. On a quarterly basis, Teradyne evaluates the realizability of the deferred tax assets by jurisdiction and assesses the need for a valuation allowance. As of March 31, 2019, Teradyne believes that it will ultimately realize the deferred tax assets recorded on the condensed consolidated balance sheet. However, should Teradyne believe that it is more-likely-than-not that the deferred tax assets would not be realized, the tax provision would increase in the period in which Teradyne determined that the realizability was not likely. Teradyne considers the probability of future taxable income and historical profitability, among other factors, in assessing the realizability of the deferred tax assets. As of March 31, 2019 and December 31, 2018, Teradyne had $13.5 million and $43.4 million, respectively, of reserves for uncertain tax positions. The $29.9 million net decrease in reserves for uncertain tax positions is composed of reductions in uncertain tax positions amounting to $22.4 million related to transfer pricing and $7.4 million associated with U.S. research and development tax credits. These reductions resulted from the conclusion of the U.S. Federal income tax audit for the year ended December 31, 2015. As of March 31, 2019, Teradyne estimates that it is reasonably possible that the balance of unrecognized tax benefits may decrease approximately $0.2 million in the next twelve months, as a result of a lapse of statutes of limitation. The estimated decrease is composed of reserves relating to local tax incentives. Teradyne recognizes interest and penalties related to income tax matters in income tax expense. As of March 31, 2019 and December 31, 2018, $0.6 million and $0.3 million, respectively, of interest and penalties were accrued for uncertain tax positions. For the three months ended March 31, 2019 and April 1, 2018, expense of $0.3 million and $0.1 million, respectively, was recorded for interest and penalties related to income tax items. Teradyne qualifies for a tax holiday in Singapore by fulfilling the requirements of an agreement with the Singapore Economic Development Board under which certain headcount and spending requirements must be met. The tax savings due to the tax holiday for the three months ended March 31, 2019 was $2.1 million, or $0.01 per diluted share. The tax savings due to the tax holiday for the three months ended April 1, 2018 was $3.0 million, or $0.01 per diluted share. The tax holiday is scheduled to expire on December 31, 2020.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Segment Information	U. SEGMENT INFORMATION Teradyne has four reportable segments (Semiconductor Test, System Test, Industrial Automation and Wireless Test). Each of the Semiconductor Test, System Test, and Wireless Test segments is also an individual operating segment. The Industrial Automation reportable segment consists of operating segments with discrete financial information, which have been combined into one reportable segment as they share similar economic characteristics, types of products, production processes, distribution channels, and currency risks. The Semiconductor Test segment includes operations related to the design, manufacturing and marketing of semiconductor test products and services. The System Test segment includes operations related to the design, manufacturing and marketing of products and services for defense/aerospace instrumentation test, storage test and circuit-board test. The Industrial Automation segment includes operations related to the design, manufacturing and marketing of collaborative robotic arms, autonomous mobile robots and advanced robotic control software. The Wireless Test segment includes operations related to the design, manufacturing and marketing of wireless test products and services. Teradyne evaluates performance based on several factors, of which the primary financial measure is business segment income (loss) before income taxes. The accounting policies of the business segments in effect are described in Note B: “Accounting Policies” in Teradyne’s Annual Report on Form 10-K for the year ended December 31, 2018. Segment information for the three months ended March 31, 2019 and April 1, 2018 is as follows: Semiconductor Test Industrial Automation System Test Wireless Test Corporate and Other Consolidated (in thousands) Three Months Ended March 31, 2019 Revenues $ 340,853 $ 66,136 $ 58,220 $ 29,041 $ (151 ) $ 494,099 Income (loss) before income taxes (1)(2) 83,049 5,295 15,340 3,628 2,743 93,979 Total assets (3) 770,967 596,899 98,916 73,066 1,076,795 2,616,643 Three Months Ended April 1, 2018 Revenues $ 373,328 $ 48,834 $ 43,019 $ 22,507 $ (221 ) $ 487,467 Income before income taxes (1)(2) 88,079 784 5,888 464 605 95,820 Total assets (3) 758,737 406,557 90,785 59,739 1,679,375 2,995,193 (1) Included in Corporate and Other are: contingent consideration adjustments, severance charges, interest income, interest expense, net foreign exchange gains (losses), intercompany eliminations and acquisition related charges. (2) Included in the income (loss) before income taxes for each of the segments are charges and credits related to restructuring and other and inventory charges. (3) Total business assets are directly attributable to each business. Corporate assets consist of cash and cash equivalents, marketable securities and certain other assets. Included in the Semiconductor Test segment are charges in the following line items in the statements of operations: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Cost of revenues—inventory charge $ 1,174 $ 2,166 Restructuring and other—employee severance 567 3,761 Included in the Industrial Automation segment are charges in the following line items in the statements of operations: For the Three Months March 31, 2019 April 1, 2018 (in thousands) Restructuring and other—acquisition related expenses and compensation $ 1,261 $ — Cost of revenues—inventory charge 416 200 Included in the System Test segment are charges in the following line item in the statements of operations: For the Three Months Ended March 31, April 1, (in thousands) Cost of revenues—inventory charge $ 468 $ 320 Included in the Wireless Test segment are charges in the following line items in the statements of operations: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Cost of revenues—inventory charge $ 339 $ 836 Included in Corporate and Other are charges and credits in the following line items in the statements of operations: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Restructuring and other—MiR contingent consideration adjustment $ 3,003 $ — Restructuring and other—Universal Robots contingent consideration adjustment — (4,968 ) Restructuring and other—acquisition related expenses — 774

Shareholders' Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	V. SHAREHOLDERS’ EQUITY Stock Repurchase Program In January 2018, Teradyne’s Board of Directors cancelled the December 2016 stock repurchase program and authorized a new stock repurchase program for up to $1.5 billion of common stock. Teradyne intends to repurchase $500 million in 2019. During the three months ended March 31, 2019, Teradyne repurchased 4.5 million shares of common stock for $156.5 million at an average price of $35.12 per During the three months ended , Teradyne repurchased million shares of common stock for $ million at an average price of $ per share. The total price includes commissions and is recorded as a reduction to retained earnings. Dividend Holders of Teradyne’s common stock are entitled to receive dividends when they are declared by Teradyne’s Board of Directors. In January 2019, Teradyne’s Board of Directors declared a quarterly cash dividend of $0.09 per share. Dividend payments for the three months ended March 31, 2019 were $15.6 million. In January 2018, Teradyne’s Board of Directors declared a quarterly cash dividend of $0.09 per share. Dividend payments for the three months ended April 1, 2018 were $17.6 million. While Teradyne declared a quarterly cash dividend and authorized a share repurchase program, it may reduce or eliminate the cash dividend or share repurchase program in the future. Future cash dividends and stock repurchases are subject to the discretion of Teradyne’s Board of Directors, which will consider, among other things, Teradyne’s earnings, capital requirements and financial condition.

Accounting Policies (Policies)

Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Basis of Presentation	Basis of Presentation The consolidated interim financial statements include the accounts of Teradyne and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated. These interim financial statements are unaudited and reflect all normal recurring adjustments that are, in the opinion of management, necessary for the fair statement of such interim financial statements. Certain prior year amounts were reclassified to conform to the current year presentation. The December 31, 2018 condensed consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America. The accompanying financial information should be read in conjunction with the consolidated financial statements and notes thereto contained in Teradyne’s Annual Report on Form 10-K, filed with the U.S. Securities and Exchange Commission (“SEC”) on March 1, 2019, for the year ended December 31, 2018.
Preparation of Financial Statements and Use of Estimates	Preparation of Financial Statements and Use of Estimates The preparation of consolidated financial statements requires management to make estimates and judgments that affect the amounts reported in the financial statements. Actual results may differ significantly from these estimates.
Leases	Leases In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, “Leases (Topic 842)” “Leases (Topic 842): Targeted Improvements,” Under ASC 842, a contract is or contains a lease when Teradyne has the right to control the use of an identified asset. Teradyne determines if an arrangement is a lease at inception of the contract, which is the date on which the terms of the contract are agreed to and the agreement creates enforceable rights and obligations. The commencement date of the lease is the date that the lessor makes an underlying asset available for use by Teradyne. As of March 31, 2019, Teradyne does not have material leases that have not yet commenced. Teradyne determines if the lease is operating or finance at the lease commencement date based upon the terms of the lease and the nature of the asset. The lease term used to calculate the lease liability includes options to extend or terminate the lease when it is reasonably certain that the option will be exercised. For leases commencing after January 1, 2019, the lease liability is measured at the present value of future lease payments, discounted using the discount rate for the lease at the commencement date. As Teradyne is typically unable to determine the implicit rate, Teradyne uses an incremental borrowing rate based on the lease term and economic environment at commencement date. Teradyne initially measures payments based on an index by using the applicable rate at lease commencement. Variable payments that do not depend on an index are not included in the lease liability and are recognized as they are incurred. The ROU asset is initially measured as the amount of lease liability, adjusted for any initial lease costs, prepaid lease payments, and reduced by any lease incentives. Teradyne’s contracts often include non-lease components such as common area maintenance. Teradyne elected the practical expedient to account for the lease and non-lease components as a single lease component. For leases with a term of one year or less Teradyne has elected not to record the lease asset or liability. The lease payments are recognized in the consolidated statement of earnings on a straight-line basis over the lease term. Teradyne includes lease costs within cost of revenues and operating expenses. See Note: H: “Leases.”

Acquisitions (Tables)

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2019
Final Allocation of Purchase Price	The following table represents the final allocation of the purchase price: Purchase Price Allocation (in thousands) Goodwill $ 135,976 Intangible assets 80,670 Tangible assets acquired and liabilities assumed: Current assets 6,039 Non-current assets 1,336 Accounts payable and current liabilities (7,336 ) Long-term deferred tax liabilities (18,007 ) Other long-term liabilities (900 ) Total purchase price $ 197,778
Components of Intangible Assets and Their Estimated Useful Lives at Acquisition Date	Components of these intangible assets and their estimated useful lives at the acquisition date are as follows: Fair Value Estimated Useful Life (in thousands) (in years) Developed technology $ 58,900 7.0 Trademarks and tradenames 13,240 11.0 Customer relationships 8,500 2.5 Backlog 30 0.2 Total intangible assets $ 80,670 7.2
Pro Forma Results Under Acquisitions	The unaudited pro forma results are not necessarily indicative of what actually would have occurred had the acquisition been in effect for the periods presented: For the Three Months Ended April 1, 2018 (in thousands) Revenue $ 493,017 Net income 85,151 Net income per common share: Basic $ 0.44 Diluted $ 0.42

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregated Revenue by Primary Geographical Market, Major Product Line and Timing of Revenue Recognition	The following table provides information about disaggregated revenue by primary geographical market, major product line and timing of revenue recognition. For the Three Months Ended March 31, 2019 Semiconductor Test System Test Industrial Automation Wireless Corporate Other Consolidated System on a Chip Memory Defense/ Aerospace Storage Production Universal Mobile Energid (in thousands) Americas Point in time $ 7,977 $ 8,051 $ 14,783 $ 1,593 $ 3,254 $ 15,297 $ 3,539 $ — $ 2,090 $ (151 ) $ 56,433 Over time 8,190 712 6,450 — 729 246 — 260 151 — 16,738 Europe, Middle East and Africa Point in time 11,032 153 39 — 5,064 25,904 3,840 — 736 — 46,768 Over time 5,281 280 469 — 1,554 416 — 289 45 — 8,334 Asia Pacific Point in time 219,746 35,571 263 16,605 3,636 14,178 1,727 — 24,628 — 316,354 Over time 38,913 3,280 764 2,054 920 228 — 212 1,359 — 47,730 Lease Revenue 1,667 — — — 43 — — — 32 — 1,742 Total $ 292,806 $ 48,047 $ 22,768 $ 20,252 $ 15,200 $ 56,269 $ 9,106 $ 761 $ 29,041 $ (151 ) $ 494,099 For the Three Months Ended April 1, 2018 Semiconductor Test System Test Industrial Automation Wireless Corporate Other Consolidated System on a Chip Memory Defense/ Aerospace Storage Production Universal Mobile Energid (in thousands) Americas Point in time $ 9,600 $ 2,862 $ 11,597 $ 279 $ 1,760 $ 14,373 $ — $ — $ 4,979 $ (221 ) $ 45,229 Over time 8,791 696 6,188 — 757 89 — — 112 — 16,633 Europe, Middle East and Africa Point in time 12,125 139 1,497 — 4,037 22,573 — — 1,041 — 41,412 Over time 5,214 269 551 — 1,559 143 — — 227 — 7,963 Asia Pacific Point in time 224,851 66,273 101 10,122 1,861 11,583 — — 13,664 — 328,455 Over time 36,338 2,323 208 1,533 735 73 — — 2,296 — 43,506 Lease Revenue 3,847 — — — 234 — — — 188 — 4,269 Total $ 300,766 $ 72,562 $ 20,142 $ 11,934 $ 10,943 $ 48,834 $ — $ — $ 22,507 $ (221 ) $ 487,467

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2019
Composition of Inventories, Net	Inventories, net consisted of the following at March 31, 2019 and December 31, 2018: March 31, December 31, 2019 2018 (in thousands) Raw material $ 94,862 $ 89,365 Work-in-process 29,725 31,014 Finished goods 36,755 33,162 $ 161,342 $ 153,541

Financial Instruments (Tables)

Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
Schedule of Fair Value of Financial Assets and Liabilities Measured on Recurring Basis	The following table sets forth by fair value hierarchy Teradyne’s financial assets and liabilities that were measured at fair value on a recurring basis as of March 31, 2019 and December 31, 2018. March 31, 2019 Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in thousands) Assets Cash $ 222,714 $ — $ — $ 222,714 Cash equivalents 186,520 74,494 — 261,014 Available-for-sale securities: U.S. Treasury securities — 191,043 — 191,043 Commercial paper — 180,604 — 180,604 Corporate debt securities — 91,244 — 91,244 Certificates of deposit and time deposits — 11,496 — 11,496 U.S. government agency securities — 9,629 — 9,629 Debt mutual funds 3,331 — — 3,331 Non-U.S. government securities — 378 — 378 Equity securities: Mutual funds 25,289 — — 25,289 $ 437,854 $ 558,888 $ — $ 996,742 Derivative assets — 17 — 17 Total $ 437,854 $ 558,905 $ — $ 996,759 Liabilities Contingent consideration $ — $ — $ 38,313 $ 38,313 Derivative liabilities — 291 — 291 Total $ — $ 291 $ 38,313 $ 38,604 Reported as follows: (Level 1) (Level 2) (Level 3) Total (in thousands) Assets Cash and cash equivalents $ 409,234 $ 74,494 $ — $ 483,728 Marketable securities — 421,088 — 421,088 Long-term marketable securities 28,620 63,306 — 91,926 Prepayments — 17 — 17 Total $ 437,854 $ 558,905 $ — $ 996,759 Liabilities Other current liabilities $ — $ 291 $ — $ 291 Contingent consideration — — 22,803 22,803 Long-term contingent consideration — — 15,510 15,510 Total $ — $ 291 $ 38,313 $ 38,604 December 31, 2018 Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in thousands) Assets Cash $ 312,512 $ — $ — $ 312,512 Cash equivalents 253,525 360,715 — 614,240 Available-for-sale securities: U.S. Treasury securities — 109,721 — 109,721 Commercial paper — 86,117 — 86,117 Corporate debt securities — 40,020 — 40,020 U.S. government agency securities — 9,611 — 9,611 Certificates of deposit and time deposits — 7,604 — 7,604 Debt mutual funds 3,187 — — 3,187 Non-U.S. government securities — 376 — 376 Equity securities: Mutual funds 21,191 — — 21,191 $ 590,415 $ 614,164 $ — $ 1,204,579 Derivative assets — 79 — 79 Total $ 590,415 $ 614,243 $ — $ 1,204,658 Liabilities Contingent consideration $ — $ — $ 70,543 $ 70,543 Derivative liabilities — 514 — 514 Total $ — $ 514 $ 70,543 $ 71,057 Reported as follows: (Level 1) (Level 2) (Level 3) Total (in thousands) Assets Cash and cash equivalents $ 566,037 $ 360,715 $ — $ 926,752 Marketable securities — 190,096 — 190,096 Long-term marketable securities 24,378 63,353 — 87,731 Prepayments — 79 — 79 Total $ 590,415 $ 614,243 $ — $ 1,204,658 Liabilities Other accrued liabilities $ — $ 514 $ — $ 514 Contingent consideration — — 34,865 34,865 Long-term contingent consideration — — 35,678 35,678 Total $ — $ 514 $ 70,543 $ 71,057
Schedule of Changes in Fair Value of Level 3 Contingent Consideration	Changes in the fair value of Level 3 contingent consideration for the three months ended March 31, 2019 and April 1, 2018 were as follows: For the Three Months Ended March 31, April 1, 2019 2018 (in thousands) Balance at beginning of period $ 70,543 $ 45,102 Foreign currency impact (610 ) — Payments (a) (34,590 ) (24,553 ) Fair value adjustment (b) 2,970 (4,968 ) Balance at end of period $ 38,313 $ 15,581 (a) In the three months ended March 31, 2019, Teradyne paid $ 30.8 $ 24.6 (b) In the three months ended March 31, 2019, the fair value of contingent consideration for the earn-out in connection with the acquisition of MiR was increased by $ 3.0 $ 5.0
Quantitative Information Associated With Fair Value Measurement of Level 3 Financial Instrument	The following table provides quantitative information associated with the fair value measurement of Teradyne’s Level 3 financial instruments: Liability March 31, 2019 Fair Value Valuation Technique Unobservable Inputs Weighted Average (in thousands) Contingent consideration (MiR) $ 38,313 Monte Carlo Simulation Revenue volatility 17.0 % Discount Rate 0.4 %
Schedule of Carrying Amounts and Fair Values of Financial Instruments	The carrying amounts and fair values of Teradyne’s financial instruments at March 31, 2019 and December 31, 2018 were as follows: March 31, 2019 December 31, 2018 Carrying Value Fair Value Carrying Value Fair Value (in thousands) Assets Cash and cash equivalents $ 483,728 $ 483,728 $ 926,752 $ 926,752 Marketable securities 513,014 513,014 277,827 277,827 Derivative assets 17 17 79 79 Liabilities Contingent consideration 38,313 38,313 70,543 70,543 Derivative liabilities 291 291 514 514 Convertible debt (1) 383,590 644,575 379,981 547,113 (1) The carrying value represents the bifurcated debt component only, while the fair value is based on quoted market prices for the convertible note, which includes the equity conversion features.
Schedule of Available-for-Sale Marketable Securities	The following table summarizes the composition of available-for-sale marketable securities at March 31, 2019: March 31, 2019 Available-for-Sale Cost Unrealized Gain Unrealized (Loss) Fair Market Value Fair Market Value of Investments with Unrealized Losses (in thousands) U.S. Treasury securities $ 191,715 $ 144 $ (816 ) $ 191,043 $ 82,132 Commercial paper 180,610 1 (7 ) 180,604 11,237 Corporate debt securities 90,402 1,343 (501 ) 91,244 18,150 Certificates of deposit and time deposits 11,497 1 (2 ) 11,496 4,419 U.S. government agency securities 9,646 4 (21 ) 9,629 4,101 Debt mutual funds 3,255 76 — 3,331 — Non-U.S. government securities 378 — — 378 — $ 487,503 $ 1,569 $ (1,347 ) $ 487,725 $ 120,039 Reported as follows: Cost Unrealized Gain Unrealized (Loss) Fair Value Fair Market Value of Investments with Unrealized Losses (in thousands) Marketable securities $ 421,024 $ 126 $ (62 ) $ 421,088 $ 91,100 Long-term marketable securities 66,479 1,443 (1,285 ) 66,637 28,939 $ 487,503 $ 1,569 $ (1,347 ) $ 487,725 $ 120,039 The following table summarizes the composition of available-for-sale marketable securities at December 31, 2018: December 31, 2018 Available-for-Sale Cost Unrealized Gain Unrealized (Loss) Fair Value Market Fair Market Value of Investments with Unrealized Losses (in thousands) U.S. Treasury securities $ 110,969 $ 112 $ (1,360 ) $ 109,721 $ 75,040 Commercial paper 86,130 13 (26 ) 86,117 85,094 Corporate debt securities 41,133 432 (1,545 ) 40,020 24,767 U.S. government agency securities 9,646 1 (36 ) 9,611 7,077 Certificates of deposit and time deposits 7,604 — — 7,604 — Debt mutual funds 3,153 34 — 3,187 — Non-U.S. government securities 376 — — 376 — $ 259,011 $ 592 $ (2,967 ) $ 256,636 $ 191,978 Reported as follows: Cost Unrealized Gain Unrealized (Loss) Fair Value Market Fair Market Value of Investments with Unrealized Losses (in thousands) Marketable securities $ 190,100 $ 88 $ (92 ) $ 190,096 $ 140,262 Long-term marketable securities 68,911 504 (2,875 ) 66,540 51,716 $ 259,011 $ 592 $ (2,967 ) $ 256,636 $ 191,978
Contractual Maturities of Investments Held	The contractual maturities of investments in available-for-sale securities held at March 31, 2019 were as follows: March 31, 2019 Cost Fair Market Value (in thousands) Due within one year $ 421,024 $ 421,088 Due after 1 year through 5 years 9,325 9,343 Due after 5 years through 10 years 14,026 13,659 Due after 10 years 39,873 40,304 Total $ 484,248 $ 484,394
Schedule of Derivative Instruments in Statement of Financial Position at Fair Value	The following table summarizes the fair value of derivative instruments as of March 31, 2019 and December 31, 2018: Balance Sheet Location March 31, December 31, (in thousands) Derivatives not designated as hedging instruments: Foreign exchange contracts Prepayments $ 17 $ 79 Foreign exchange contracts Other current liabilities (291 ) (514 ) Total derivatives $ (274 ) $ (435 )
Schedule of Effect of Derivative Instruments on Statement of Operations Recognized	The following table summarizes the effect of derivative instruments recognized in the statement of operations for the three months ended March 31, 2019 and April 1, 2018. Location of Losses (Gains) For the Three Months Ended Recognized in March 31, April 1, Statement of Operations 2019 2018 (in thousands) Derivatives not designated as hedging instruments: Foreign exchange contracts Other (income) expense, net $ 3,934 $ 1,575 (1) The table does not reflect the corresponding gains and losses from the remeasurement of monetary assets and liabilities denominated in foreign currencies. (2) For the three months ended March 31, 2019 and April 1, 2018, net gains from the remeasurement of monetary assets and liabilities denominated in foreign currencies were $ 3.2 0.6

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Supplemental cash flow information related to leases	Supplemental cash flow information related to leases was as follows: For the Three Months March 31, (in thousands) Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows $ 5,059 Right-of-use assets obtained in exchange for new lease obligations 5,737
Schedule of operating lease, maturity	Maturities of lease liabilities as of March 31, 2019 were as follows: Operating Leases (in thousands) 2019 $ 15,375 2020 18,967 2021 14,514 2022 10,262 2023 5,719 Thereafter 11,484 Total lease payments 76,321 Less imputed interest (21,083 ) Total lease liabilities $ 55,238
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	As of December 31, 2018, future non-cancelable rent obligations as determined under ASC 840 were as follows: Operating Leases (in thousands) 2019 $ 19,570 2020 18,293 2021 13,578 2022 9,693 2023 5,449 Thereafter 9,472 Total lease payments $ 76,055

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Components of Convertible Senior Notes	The below tables represent the key components of Teradyne’s convertible senior notes: March 31, 2019 December 31, 2018 (in thousands) Debt Principal $ 460,000 $ 460,000 Unamortized discount 76,410 80,019 Net Carrying amount of convertible debt $ 383,590 $ 379,981 For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Contractual interest expense on the coupon $ 1,438 $ 1,438 Amortization of the discount component recognized as interest expense 3,608 3,434 Total interest expense on the convertible debt $ 5,046 $ 4,872

Prepayments (Tables)

Prepayments (Tables)	3 Months Ended
	Mar. 31, 2019
Schedule of Prepayments and other assets	Prepayments consist of the following and are included in prepayments and other assets on the balance sheet: March 31, December 31, 2019 2018 (in thousands) Contract manufacturer and supplier prepayments $ 147,015 $ 131,642 Prepaid taxes 13,404 9,646 Prepaid maintenance and other services 7,703 8,487 Other prepayments 16,111 12,744 Total prepayments $ 184,233 $ 162,519

Deferred Revenue and Customer_2

Deferred Revenue and Customer Advances (Tables)	3 Months Ended
	Mar. 31, 2019
Deferred Revenue and Customer Advances	Deferred revenue and customer advances consist of the following and are included in short and long-term deferred revenue and customer advances on the balance sheet: March 31, December 31, 2019 2018 (in thousands) Maintenance and training $ 58,394 $ 58,362 Extended warranty 27,242 27,422 Customer advances, undelivered performance obligations and other 31,971 24,677 Total deferred revenue and customer advances $ 117,607 $ 110,461

Product Warranty (Tables)

Product Warranty (Tables)	3 Months Ended
	Mar. 31, 2019
Other Accrued Liabilities	The warranty balance below is included in other accrued liabilities on the balance sheet. For the Three Months Ended March 31, April 1, 2019 2018 (in thousands) Balance at beginning of period $ 7,909 $ 8,200 Acquisition 14 — Accruals for warranties issued during the period 3,066 3,063 Accruals related to pre-existing warranties 1,330 (139 ) Settlements made during the period (4,567 ) (3,576 ) Balance at end of period $ 7,752 $ 7,548
Extended Product Warranty of Short and Long-Term Deferred Revenue and Customer Advances	The balance below is included in short and long-term deferred revenue and customer advances on the balance sheet. For the Three Months Ended March 31, April 1, 2019 2018 (in thousands) Balance at beginning of period $ 27,422 $ 24,438 Deferral of new extended warranty revenue 5,820 5,139 Recognition of extended warranty deferred revenue (6,000 ) (4,987 ) Balance at end of period $ 27,242 $ 24,590

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2019
Schedule of Estimated Fair Value of TSR Performance-Based Restricted Stock Unit Awards Assumptions	The fair value was estimated using the Monte Carlo simulation model with the following assumptions: For the Three Months Ended March 31, April 1, 2019 2018 Risk-free interest rate 2.6 % 2.2 % Teradyne volatility-historical 31.8 % 26.8 % NYSE Composite Index volatility-historical 12.0 % 12.4 % Dividend yield 1.0 % 0.8 %
Fair Value of Stock Options Using Assumptions	The fair value of stock options was estimated using the Black-Scholes option-pricing model with the following assumptions: For the Three Months Ended March 31, April 1, 2019 2018 Expected life (years) 5.0 5.0 Risk-free interest rate 2.6 % 2.4 % Volatility-historical 30.1 % 26.4 % Dividend yield 1.0 % 0.8 %

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2019
Changes in Accumulated Other Comprehensive (Loss) Income	Changes in accumulated other comprehensive income (loss), which are presented net of tax, consist of the following: Foreign Currency Translation Adjustment Unrealized Gains (Losses) on Marketable Securities Retirement Plans Prior Service Credit Total (in thousands) Three Months Ended March 31, 2019 Balance at December 31, 2018, net of tax of $0, $(521), $(1,081), respectively $ (12,523 ) $ (1,845 ) $ 1,328 $ (13,040 ) Other comprehensive income before reclassifications, net of tax of $0, $577, $0, respectively (4,659 ) 2,100 — (2,559 ) Amounts reclassified from accumulated other comprehensive income, net of tax of $0, $(20), $(11), respectively — (70 ) (37 ) (107 ) Net current period other comprehensive income (loss), net of tax o f $0, $557, $(11), respectively (4,659 ) 2,030 (37 ) (2,666 ) Balance at March 31, 2019, net of tax of $0, $36, $(1,092), respectively $ (17,182 ) $ 185 $ 1,291 $ (15,706 ) Foreign Currency Translation Adjustments Unrealized Gains (Losses) on Marketable Securities Retirement Plans Prior Service Credit Total (in thousands) Three Months Ended April 1, 2018 Balance at December 31, 2017, net of tax of $0, $1,815, $(932), respectively $ 15,919 $ 1,362 $ 1,495 $ 18,776 Other comprehensive income (loss) before reclassifications, net of tax of $0, $(718), $0, respectively 10,541 (2,687 ) — 7,854 Amounts reclassified from accumulated other comprehensive income, net of tax of $0, $78, $(18), respectively — 1,668 (61 ) 1,607 Net current period other comprehensive income (loss), net of tax of $0, $(640), $(18), respectively 10,541 (1,019 ) (61 ) 9,461 Reclassification of income tax effects from the Tax Reform Act, net of tax of $0, $(691), $(78), respectively (a) — 691 78 769 Reclassification of unrealized gains on equity securities, net of tax of $0, $(902), $0, respectively (b) — (3,125 ) — (3,125 ) Balance as April 1, 2018, net of tax of $0, $(418), $(1,028), respectively $ 26,460 $ (2,091 ) $ 1,512 $ 25,881 (a) In the three months ended , Teradyne early adopted the ASU 2018-02, “Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” (b) 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
Reclassifications Out of Accumulated Other Comprehensive Income to Statements of Operations	Reclassifications out of accumulated other comprehensive income (loss) to the statement of operations for the three months ended March 31, 2019 and April 1, 2018 were as follows: Details about Accumulated Other Comprehensive Income Components For the Three Months Ended Affected Line Item in the Statements of Operations March 31, April 1, 018 (in thousands) Available-for-sale marketable securities: Unrealized gains (losses), net of tax of $ 20 78 $ 70 $ (1,668 ) Interest (expense) income Defined benefit pension and postretirement plans: Amortization of prior service benefit, net of tax of $ 11 18 37 61 (a) Total reclassifications, net of tax of $ 31 60 $ 107 $ (1,607 ) Net income (a) The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit. See Note R: “Retirement Plans.”

Goodwill and Acquired Intangi_2

Goodwill and Acquired Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2019
Changes in Carrying Amount of Goodwill by Segment	The changes in the carrying amount of goodwill by reportable segments for the three months ended March 31, 2019, were as follows: Industrial Automation System Test Wireless Test Semiconductor Test Total (in thousands) Balance at December 31, 2018 Goodwill $ 363,358 $ 158,699 $ 361,819 $ 260,540 $ 1,144,416 Accumulated impairment losses — (148,183 ) (353,843 ) (260,540 ) (762,566 ) 363,358 10,516 7,976 — 381,850 Lemsys acquisition — — — 1,145 1,145 Foreign currency translation adjustment (3,494 ) — — 12 (3,482 ) Balance at March 31, 2019 Goodwill 359,864 158,699 361,819 261,697 1,142,079 Accumulated impairment losses — (148,183 ) (353,843 ) (260,540 ) (762,566 ) $ 359,864 $ 10,516 $ 7,976 $ 1,157 $ 379,513
Schedule of Amortizable Intangible Assets	Amortizable intangible assets consist of the following and are included in intangible assets, net on the balance sheet: March 31, 2019 Gross Carrying Amount (1) Accumulated Amortization Foreign Translation Adjustment Net Carrying Amount (in thousands) Developed technology $ 337,218 $ (259,129 ) $ (4,812 ) $ 73,277 Customer relationships 100,743 (85,469 ) (408 ) 14,866 Tradenames and trademarks 64,670 (32,897 ) (973 ) 30,800 Non-compete agreement 320 (320 ) — — Backlog 780 (349 ) (2 ) 429 Total intangible assets $ 503,731 $ (378,164 ) $ (6,195 ) $ 119,372 December 31, 2018 Gross Carrying Amount Accumulated Amortization Foreign Translation Adjustment Net Carrying Amount (in thousands) Developed technology $ 336,308 $ (252,080 ) $ (4,079 ) $ 80,149 Customer relationships 97,153 (83,448 ) (340 ) 13,365 Tradenames and trademarks 64,420 (31,653 ) (799 ) 31,968 Non-compete agreement 320 (320 ) — — Backlog 30 (30 ) — — Total intangible assets $ 498,231 $ (367,531 ) $ (5,218 ) $ 125,482 (1) Includes $5.5 million of intangible assets
Schedule of Estimated Intangible Assets Amortization Expense	Estimated intangible asset amortization expense for each of the five succeeding fiscal years is as follows: Year Amortization Expense (in thousands) 2019 (remainder) 29,184 2020 24,852 2021 14,707 2022 13,815 2023 13,339 Thereafter 23,475

Net Income Per Common Share (Ta

Net Income Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2019
Computation of Basic and Diluted Net Income (Loss) Per Common Share	The following table sets forth the computation of basic and diluted net income per common share: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands, except per share amounts) Net income for basic and diluted net income per share $ 109,138 $ 86,974 Weighted average common shares-basic 173,532 195,255 Effect of dilutive potential common shares: Incremental shares from assumed conversion of convertible notes (1) 2,186 4,398 Convertible note hedge warrant shares (2) — 1,830 Restricted stock units 1,021 1,666 Stock options 222 321 Employee stock purchase plan 11 14 Dilutive potential common shares 3,440 8,229 Weighted average common shares-diluted 176,972 203,484 Net income per common share-basic $ 0.63 $ 0.45 Net income per common share-diluted $ 0.62 $ 0.43 (1) Incremental shares from assumed conversion of the convertible notes was calculated using the difference between the average Teradyne stock price for the period and the conversion price of $31.70, multiplied by 14.5 million shares. The result of this calculation, representing the total intrinsic value of the convertible debt, was divided by the average Teradyne stock price for the period. (2) Convertible notes hedge warrant shares were calculated using the difference between the average Teradyne stock price for the period and the warrant price of $39.78, multiplied by 14.5 million shares. The result of this calculation, representing the total intrinsic value of the warrant, was divided by the average Teradyne stock price for the period.

Retirement Plans (Tables)

Retirement Plans (Tables)	3 Months Ended
	Mar. 31, 2019
Defined Benefit Pension Plans
Net Periodic Pension and Postretirement Benefit Costs	For the three months ended March 31, 2019 and April 1, 2018, Teradyne’s net periodic pension cost was comprised of the following: For the Three Months Ended March 31, 2019 April 1, 2018 United States Foreign United States Foreign (in thousands) Service cost $ 405 $ 188 $ 571 $ 213 Interest cost 1,795 173 2,997 186 Expected return on plan assets (1,511 ) (7 ) (3,369 ) (5 ) Amortization of prior service cost — — 14 — Total net periodic pension cost $ 689 $ 354 $ 213 $ 394
Postretirement Benefit Plans
Net Periodic Pension and Postretirement Benefit Costs	For the three months ended March 31, 2019 and April 1, 2018, Teradyne’s net periodic postretirement benefit cost was comprised of the following: For the Three March 31, April 1, 2018 (in thousands) Service cost $ 9 $ 9 Interest cost 85 50 Amortization of prior service credit (48 ) (93 ) Special termination benefits — 1,626 Total net periodic postretirement benefit cost $ 46 $ 1,592

Segment Information (Table)

Segment Information (Table)	3 Months Ended
	Mar. 31, 2019
Segment Information	Segment information for the three months ended March 31, 2019 and April 1, 2018 is as follows: Semiconductor Test Industrial Automation System Test Wireless Test Corporate and Other Consolidated (in thousands) Three Months Ended March 31, 2019 Revenues $ 340,853 $ 66,136 $ 58,220 $ 29,041 $ (151 ) $ 494,099 Income (loss) before income taxes (1)(2) 83,049 5,295 15,340 3,628 2,743 93,979 Total assets (3) 770,967 596,899 98,916 73,066 1,076,795 2,616,643 Three Months Ended April 1, 2018 Revenues $ 373,328 $ 48,834 $ 43,019 $ 22,507 $ (221 ) $ 487,467 Income before income taxes (1)(2) 88,079 784 5,888 464 605 95,820 Total assets (3) 758,737 406,557 90,785 59,739 1,679,375 2,995,193 (1) Included in Corporate and Other are: contingent consideration adjustments, severance charges, interest income, interest expense, net foreign exchange gains (losses), intercompany eliminations and acquisition related charges. (2) Included in the income (loss) before income taxes for each of the segments are charges and credits related to restructuring and other and inventory charges. (3) Total business assets are directly attributable to each business. Corporate assets consist of cash and cash equivalents, marketable securities and certain other assets.
Semiconductor Test
Schedule of Segment Reporting Information by Segment Charges	Included in the Semiconductor Test segment are charges in the following line items in the statements of operations: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Cost of revenues—inventory charge $ 1,174 $ 2,166 Restructuring and other—employee severance 567 3,761
Industrial Automation
Schedule of Segment Reporting Information by Segment Charges	Included in the Industrial Automation segment are charges in the following line items in the statements of operations: For the Three Months March 31, 2019 April 1, 2018 (in thousands) Restructuring and other—acquisition related expenses and compensation $ 1,261 $ — Cost of revenues—inventory charge 416 200
System Test
Schedule of Segment Reporting Information by Segment Charges	Included in the System Test segment are charges in the following line item in the statements of operations: For the Three Months Ended March 31, April 1, (in thousands) Cost of revenues—inventory charge $ 468 $ 320
Wireless Test
Schedule of Segment Reporting Information by Segment Charges	Included in the Wireless Test segment are charges in the following line items in the statements of operations: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Cost of revenues—inventory charge $ 339 $ 836
Corporate and Other [Member]
Schedule of Segment Reporting Information by Segment Charges	Included in Corporate and Other are charges and credits in the following line items in the statements of operations: For the Three Months Ended March 31, 2019 April 1, 2018 (in thousands) Restructuring and other—MiR contingent consideration adjustment $ 3,003 $ — Restructuring and other—Universal Robots contingent consideration adjustment — (4,968 ) Restructuring and other—acquisition related expenses — 774

Accounting Policies - Additiona

Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Feb. 28, 2016
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Liability	$ 55,238	$ 54,300	$ 54,300
Operating Lease, Right-of-Use Asset	$ 50,733	$ 50,100	$ 50,100

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) - USD ($)	Apr. 25, 2018	Feb. 26, 2018	Jan. 30, 2019	Apr. 01, 2018	Mar. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Contingent consideration						$ 30,800,000
Goodwill					$ 379,513,000	$ 381,850,000
Mobile Industrial Robots (MiR)
Business Acquisition [Line Items]
Total preliminary purchase price	$ 197,778,000
Cash paid to acquire outstanding common and preferred stock	145,200,000
Contingent consideration	52,600,000
Arrangement range of outcomes value high					$ 83,200,000
Goodwill, not deductible for tax purposes	136,000,000
Net income				$ 85,151,000
Goodwill	$ 135,976,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years 2 months 12 days
Mobile Industrial Robots (MiR) | Acquisition Related Costs
Business Acquisition [Line Items]
Net income				$ 600,000
Energid Technologies Corporation
Business Acquisition [Line Items]
Total preliminary purchase price		$ 27,600,000
Goodwill		14,400,000
Acquired value of intangible assets		$ 12,300,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		7 years 8 months 12 days
Net tangible assets		$ 1,000,000
Lemsys [Member]
Business Acquisition [Line Items]
Total preliminary purchase price			$ 1,200,000
Total preliminary purchase price			9,100,000
Acquired value of intangible assets			$ 5,500,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			4 years 10 months 24 days
Net tangible assets			$ 2,400,000

Final Allocation of Purchase Pr

Final Allocation of Purchase Price (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Apr. 25, 2018
Business Acquisition [Line Items]
Goodwill	$ 379,513	$ 381,850
Mobile Industrial Robots (MiR)
Business Acquisition [Line Items]
Goodwill			$ 135,976
Intangible assets			80,670
Current assets			6,039
Non-current assets			1,336
Accounts payable and current liabilities			(7,336)
Long-term deferred tax liabilities			(18,007)
Other long-term liabilities			(900)
Total purchase price			$ 197,778

Components of Intangible Assets

Components of Intangible Assets and Their Estimated Useful Lives at Acquisition Date (Detail) - Mobile Industrial Robots (MiR) $ in Thousands	Apr. 25, 2018USD ($)
Business Acquisition [Line Items]
Total intangible assets, fair value	$ 80,670
Total intangible assets, estimated useful life, years	7 years 2 months 12 days
Developed technology
Business Acquisition [Line Items]
Total intangible assets, fair value	$ 58,900
Total intangible assets, estimated useful life, years	7 years
Trademarks and tradenames
Business Acquisition [Line Items]
Total intangible assets, fair value	$ 13,240
Total intangible assets, estimated useful life, years	11 years
Customer Relationships
Business Acquisition [Line Items]
Total intangible assets, fair value	$ 8,500
Total intangible assets, estimated useful life, years	2 years 6 months
Customer backlog
Business Acquisition [Line Items]
Total intangible assets, fair value	$ 30
Total intangible assets, estimated useful life, years	2 months 12 days

Pro Forma Results Under Acquisi

Pro Forma Results Under Acquisition (Detail) - Mobile Industrial Robots (MiR) $ / shares in Units, $ in Thousands	3 Months Ended
	Apr. 01, 2018USD ($)$ / shares
Business Acquisition [Line Items]
Revenue | $	$ 493,017
Net income | $	$ 85,151
Net income per common share, basic | $ / shares	$ 0.44
Net income per common share, diluted | $ / shares	$ 0.42

Revenue - Additional Informatio

Revenue - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Revenue recognized in accordance with ASC 606	$ 494,099	$ 487,467
Revenue on leases	1,700	4,300
Deferred Revenue And Customer Advances	19,500	21,800
Trade Accounts Receivable	$ 41,700	3,500
Short-term Contract with Customer [Member]
Revenue, Remaining Performance Obligation, Percentage	72.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction Period	12 months
Long-term Contract with Customer [Member]
Revenue, Remaining Performance Obligation, Percentage	22.00%
Long-term Contract with Customer [Member] | Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction Period	3 years
Long-term Contract with Customer [Member] | Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction Period	1 year
Accounting Standards Update 2014-09 [Member]
Revenue recognized in accordance with ASC 606	$ 492,400	$ 483,200

Disaggregated Revenue by Primar

Disaggregated Revenue by Primary Geographical Market, Major Product Line and Timing of Revenue Recognition (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Disaggregation of Revenue [Line Items]
Total	$ 494,099	$ 487,467
Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	340,853	373,328
System Test
Disaggregation of Revenue [Line Items]
Total	58,220	43,019
Industrial Automation
Disaggregation of Revenue [Line Items]
Total	66,136	48,834
Wireless Test
Disaggregation of Revenue [Line Items]
Total	29,041	22,507
Corporate and Other
Disaggregation of Revenue [Line Items]
Total	(151)	(221)
Americas | Point in Time
Disaggregation of Revenue [Line Items]
Total	56,433	45,229
Americas | Point in Time | Wireless Test
Disaggregation of Revenue [Line Items]
Total	2,090	4,979
Americas | Point in Time | Corporate and Other
Disaggregation of Revenue [Line Items]
Total	(151)	(221)
Americas | Over Time
Disaggregation of Revenue [Line Items]
Total	16,738	16,633
Americas | Over Time | Wireless Test
Disaggregation of Revenue [Line Items]
Total	151	112
Europe, Middle East and Africa | Point in Time
Disaggregation of Revenue [Line Items]
Total	46,768	41,412
Europe, Middle East and Africa | Point in Time | Wireless Test
Disaggregation of Revenue [Line Items]
Total	736	1,041
Europe, Middle East and Africa | Over Time
Disaggregation of Revenue [Line Items]
Total	8,334	7,963
Europe, Middle East and Africa | Over Time | Wireless Test
Disaggregation of Revenue [Line Items]
Total	45	227
Asia Pacific
Disaggregation of Revenue [Line Items]
Total	1,742	4,269
Asia Pacific | Wireless Test
Disaggregation of Revenue [Line Items]
Total	32	188
Asia Pacific | Point in Time
Disaggregation of Revenue [Line Items]
Total	316,354	328,455
Asia Pacific | Point in Time | Wireless Test
Disaggregation of Revenue [Line Items]
Total	24,628	13,664
Asia Pacific | Over Time
Disaggregation of Revenue [Line Items]
Total	47,730	43,506
Asia Pacific | Over Time | Wireless Test
Disaggregation of Revenue [Line Items]
Total	1,359	2,296
SOC | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	292,806	300,766
SOC | Americas | Point in Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	7,977	9,600
SOC | Americas | Over Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	8,190	8,791
SOC | Europe, Middle East and Africa | Point in Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	11,032	12,125
SOC | Europe, Middle East and Africa | Over Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	5,281	5,214
SOC | Asia Pacific | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	1,667	3,847
SOC | Asia Pacific | Point in Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	219,746	224,851
SOC | Asia Pacific | Over Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	38,913	36,338
Memory | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	48,047	72,562
Memory | Americas | Point in Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	8,051	2,862
Memory | Americas | Over Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	712	696
Memory | Europe, Middle East and Africa | Point in Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	153	139
Memory | Europe, Middle East and Africa | Over Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	280	269
Memory | Asia Pacific | Point in Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	35,571	66,273
Memory | Asia Pacific | Over Time | Semiconductor Test
Disaggregation of Revenue [Line Items]
Total	3,280	2,323
Defense/Aerospace | System Test
Disaggregation of Revenue [Line Items]
Total	22,768	20,142
Defense/Aerospace | Americas | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	14,783	11,597
Defense/Aerospace | Americas | Over Time | System Test
Disaggregation of Revenue [Line Items]
Total	6,450	6,188
Defense/Aerospace | Europe, Middle East and Africa | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	39	1,497
Defense/Aerospace | Europe, Middle East and Africa | Over Time | System Test
Disaggregation of Revenue [Line Items]
Total	469	551
Defense/Aerospace | Asia Pacific | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	263	101
Defense/Aerospace | Asia Pacific | Over Time | System Test
Disaggregation of Revenue [Line Items]
Total	764	208
Storage Test | System Test
Disaggregation of Revenue [Line Items]
Total	20,252	11,934
Storage Test | Americas | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	1,593	279
Storage Test | Asia Pacific | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	16,605	10,122
Storage Test | Asia Pacific | Over Time | System Test
Disaggregation of Revenue [Line Items]
Total	2,054	1,533
Production Board Test | System Test
Disaggregation of Revenue [Line Items]
Total	15,200	10,943
Production Board Test | Americas | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	3,254	1,760
Production Board Test | Americas | Over Time | System Test
Disaggregation of Revenue [Line Items]
Total	729	757
Production Board Test | Europe, Middle East and Africa | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	5,064	4,037
Production Board Test | Europe, Middle East and Africa | Over Time | System Test
Disaggregation of Revenue [Line Items]
Total	1,554	1,559
Production Board Test | Asia Pacific | System Test
Disaggregation of Revenue [Line Items]
Total	43	234
Production Board Test | Asia Pacific | Point in Time | System Test
Disaggregation of Revenue [Line Items]
Total	3,636	1,861
Production Board Test | Asia Pacific | Over Time | System Test
Disaggregation of Revenue [Line Items]
Total	920	735
Universal Robots (UR) | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	56,269	48,834
Universal Robots (UR) | Americas | Point in Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	15,297	14,373
Universal Robots (UR) | Americas | Over Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	246	89
Universal Robots (UR) | Europe, Middle East and Africa | Point in Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	25,904	22,573
Universal Robots (UR) | Europe, Middle East and Africa | Over Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	416	143
Universal Robots (UR) | Asia Pacific | Point in Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	14,178	11,583
Universal Robots (UR) | Asia Pacific | Over Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	228	$ 73
Mobile Industrial Robots (MiR) | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	9,106
Mobile Industrial Robots (MiR) | Americas | Point in Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	3,539
Mobile Industrial Robots (MiR) | Europe, Middle East and Africa | Point in Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	3,840
Mobile Industrial Robots (MiR) | Europe, Middle East and Africa | Over Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	0
Mobile Industrial Robots (MiR) | Asia Pacific | Point in Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	1,727
Energid Technologies Corporation | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	761
Energid Technologies Corporation | Americas | Over Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	260
Energid Technologies Corporation | Europe, Middle East and Africa | Over Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	289
Energid Technologies Corporation | Asia Pacific | Over Time | Industrial Automation
Disaggregation of Revenue [Line Items]
Total	$ 212

Composition of Inventories, Net

Composition of Inventories, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Inventory [Line Items]
Raw material	$ 94,862	$ 89,365
Work-in-process	29,725	31,014
Finished goods	36,755	33,162
Inventories, net	$ 161,342	$ 153,541

Inventories - Additional Inform

Inventories - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Inventory [Line Items]
Inventory reserves	$ 100.9	$ 100.8

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Dec. 31, 2018
Financial Instruments and Fair Value [Line Items]
Available-for-sale securities, realized gain	$ 100,000	$ 300,000
Available-for-sale securities, realized loss	100,000	1,500,000
Unrealized loss related to equity securities	2,800,000
Available-for-sale marketable securities, Fair Market Value of Investments in debt securities with Unrealized Losses	120,039,000		$ 191,978,000
Fair market value of investments with unrealized losses greater than one year	32,900,000		28,500,000
Aggregate loss of investments with unrealized losses greater than one year	1,300,000		1,600,000
Fair market value of investments with unrealized losses less than one year	87,100,000		163,500,000
Aggregate loss of investments with unrealized losses less than one year	100,000		1,400,000
Unrealized Gain (loss) on contracts	3,200,000	$ 600,000
Debt Mutual Funds
Financial Instruments and Fair Value [Line Items]
Available for sale securities with out contractual maturity date	3,300,000
Mobile Industrial Robots (MiR)
Financial Instruments and Fair Value [Line Items]
Maximum amount of contingent consideration paid for acquisition	83,200,000
Foreign Exchange Contracts
Financial Instruments and Fair Value [Line Items]
Unrealized Gain (loss) on contracts	$ 148,800,000		$ 163,100,000

Schedule of Fair Value of Finan

Schedule of Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	$ 487,725	$ 256,636
Contingent consideration		30,800
U.S. Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	191,043	109,721
Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	180,604	86,117
Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	91,244	40,020
Certificates of Deposit and Time Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	11,496	7,604
U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	9,629	9,611
Debt Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	3,331	3,187
Non-U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	378	376
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total	996,742	1,204,579
Derivative assets	17	79
Total	996,759	1,204,658
Contingent consideration	38,313	70,543
Derivative liabilities	291	514
Total	38,604	71,057
Fair Value, Measurements, Recurring | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash and cash equivalents	222,714	312,512
Fair Value, Measurements, Recurring | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash and cash equivalents	261,014	614,240
Fair Value, Measurements, Recurring | U.S. Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	191,043	109,721
Fair Value, Measurements, Recurring | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	180,604	86,117
Fair Value, Measurements, Recurring | Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	91,244	40,020
Fair Value, Measurements, Recurring | Certificates of Deposit and Time Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities		7,604
Fair Value, Measurements, Recurring | U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	9,629	9,611
Fair Value, Measurements, Recurring | Debt Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	3,331	3,187
Fair Value, Measurements, Recurring | Non-U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	378	376
Fair Value, Measurements, Recurring | Equity Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale equity securities	25,289	21,191
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total	437,854	590,415
Total	437,854	590,415
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Fair Value, Measurements, Recurring | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash and cash equivalents	222,714	312,512
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Fair Value, Measurements, Recurring | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash and cash equivalents	186,520	253,525
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Fair Value, Measurements, Recurring | Debt Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	3,331	3,187
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Fair Value, Measurements, Recurring | Equity Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale equity securities	25,289	21,191
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total	558,888	614,164
Derivative assets	17	79
Total	558,905	614,243
Derivative liabilities	291	514
Total	291	514
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash and cash equivalents	74,494	360,715
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | U.S. Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	191,043	109,721
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	180,604	86,117
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	91,244	40,020
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Certificates of Deposit and Time Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities		7,604
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	9,629	9,611
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Debt Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Non-U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Available for sale securities	378	376
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration	38,313	70,543
Total	$ 38,313	$ 70,543

Schedule of Reported Financial

Schedule of Reported Financial Assets and Liabilities (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	$ 996,759	$ 1,204,658
Liabilities	38,604	71,057
Other Current Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	291	514
Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	483,728	926,752
Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	421,088	190,096
Long-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	91,926	87,731
Prepayments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	17	79
Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	22,803	34,865
Long Term Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	15,510	35,678
Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	437,854	590,415
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	409,234	566,037
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Long-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	28,620	24,378
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Prepayments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	558,905	614,243
Liabilities	291	514
Significant Other Observable Inputs (Level 2) | Other Current Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	291	514
Significant Other Observable Inputs (Level 2) | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	74,494	360,715
Significant Other Observable Inputs (Level 2) | Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	421,088	190,096
Significant Other Observable Inputs (Level 2) | Long-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	63,306	63,353
Significant Other Observable Inputs (Level 2) | Prepayments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	17	79
Significant Other Observable Inputs (Level 2) | Long Term Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	38,313	70,543
Significant Unobservable Inputs (Level 3) | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	22,803	34,865
Significant Unobservable Inputs (Level 3) | Long Term Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	$ 15,510	$ 35,678

Schedule of Changes in Fair Val

Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Apr. 01, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period		$ 70,543	$ 45,102
Foreign currency impact		(610)
Payments	[1]	(34,590)	(24,553)
Fair value adjustment	[2]	2,970	(4,968)
Balance at end of period		$ 38,313	$ 15,581
[1]	In the three months ended March 31, 2019, Teradyne paid $30.8 million and $3.8 million of contingent consideration for the earn-outs in connection with the acquisition of MiR and Universal Robots A/S (“Universal Robots”), respectively. In the three months ended April 1, 2018, Teradyne paid $24.6 million of contingent consideration for the earn-out in connection with the acquisition of Universal Robots.
[2]	In the three months ended March 31, 2019, the fair value of contingent consideration for the earn-out in connection with the acquisition of MiR was increased by $3.0 million. In the three months ended April 1, 2018, the fair value of contingent consideration for the earn-out in connection with the acquisition of Universal Robots was decreased by $5.0 million, primarily due to a decrease in forecasted revenue.

Schedule of Changes in Fair V_2

Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments of contingent consideration	$ 27,615	$ 13,571
Increase (decrease) in contingent consideration	2,970	(4,968)
Universal Robots (UR)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments of contingent consideration		24,600
Increase (decrease) in contingent consideration	3,000	$ 5,000
Avionics Interface Technologies, LLC | Payment One [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments of contingent consideration	30,800
Avionics Interface Technologies, LLC | Payment Two [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments of contingent consideration	$ 3,800

Quantitative Information Associ

Quantitative Information Associated With Fair Value Measurement of Level 3 Financial Instrument (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Apr. 25, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration		$ 30,800
Mobile Industrial Robots (MiR)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration			$ 52,600
Monte Carlo Simulation | Revenue for the period July 1, 2015-December 31, 2018 | Mobile Industrial Robots (MiR)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Target achievement, volatility	17.00%
Discount Rate	0.40%
Monte Carlo Simulation | Revenue for the period July 1, 2015-December 31, 2018 | Significant Unobservable Inputs (Level 3) | Mobile Industrial Robots (MiR)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration	$ 38,313

Schedule of Carrying Amounts an

Schedule of Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Marketable securities		$ 487,725	$ 256,636
Contingent consideration			30,800
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents		483,728	926,752
Marketable securities		513,014	277,827
Derivative assets		17	79
Contingent consideration		38,313	70,543
Derivative liabilities		291	514
Convertible debt	[1]	383,590	379,981
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents		483,728	926,752
Marketable securities		513,014	277,827
Derivative assets		17	79
Contingent consideration		38,313	70,543
Derivative liabilities		291	514
Convertible debt	[1]	$ 644,575	$ 547,113
[1]	The carrying value represents the bifurcated debt component only, while the fair value is based on quoted market prices for the convertible note, which includes the equity conversion features.

Schedule of Available for Sale

Schedule of Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 487,503	$ 259,011
Available-for-sale marketable securities, Unrealized Gain	1,569	592
Available-for-sale marketable securities, Unrealized (Loss)	(1,347)	(2,967)
Available-for-sale marketable securities, Fair Market Value	487,725	256,636
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	120,039	191,978
U.S. Treasury Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	191,715	110,969
Available-for-sale marketable securities, Unrealized Gain	144	112
Available-for-sale marketable securities, Unrealized (Loss)	(816)	(1,360)
Available-for-sale marketable securities, Fair Market Value	191,043	109,721
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	82,132	75,040
Commercial Paper
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	180,610	86,130
Available-for-sale marketable securities, Unrealized Gain	1	13
Available-for-sale marketable securities, Unrealized (Loss)	(7)	(26)
Available-for-sale marketable securities, Fair Market Value	180,604	86,117
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	11,237	85,094
Corporate Debt Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	90,402	41,133
Available-for-sale marketable securities, Unrealized Gain	1,343	432
Available-for-sale marketable securities, Unrealized (Loss)	(501)	(1,545)
Available-for-sale marketable securities, Fair Market Value	91,244	40,020
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	18,150	24,767
Certificates of Deposit and Time Deposits
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	11,497	7,604
Available-for-sale marketable securities, Unrealized Gain	1
Available-for-sale marketable securities, Unrealized (Loss)	(2)
Available-for-sale marketable securities, Fair Market Value	11,496	7,604
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	4,419
U.S. Government Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	9,646	9,646
Available-for-sale marketable securities, Unrealized Gain	4	1
Available-for-sale marketable securities, Unrealized (Loss)	(21)	(36)
Available-for-sale marketable securities, Fair Market Value	9,629	9,611
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	4,101	7,077
Debt Mutual Funds
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	3,255	3,153
Available-for-sale marketable securities, Unrealized Gain	76	34
Available-for-sale marketable securities, Fair Market Value	3,331	3,187
Non-U.S. Government Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	378	376
Available-for-sale marketable securities, Fair Market Value	$ 378	$ 376

Schedule of Reported Available

Schedule of Reported Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 487,503	$ 259,011
Available-for-sale marketable securities, Unrealized Gain	1,569	592
Available-for-sale marketable securities, Unrealized (Loss)	(1,347)	(2,967)
Available-for-sale marketable securities, Fair Market Value	487,725	256,636
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	120,039	191,978
Marketable securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	421,024	190,100
Available-for-sale marketable securities, Unrealized Gain	126	88
Available-for-sale marketable securities, Unrealized (Loss)	(62)	(92)
Available-for-sale marketable securities, Fair Market Value	421,088	190,096
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	91,100	140,262
Long-term marketable securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	66,479	68,911
Available-for-sale marketable securities, Unrealized Gain	1,443	504
Available-for-sale marketable securities, Unrealized (Loss)	(1,285)	(2,875)
Available-for-sale marketable securities, Fair Market Value	66,637	66,540
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	$ 28,939	$ 51,716

Contractual Maturities of Inves

Contractual Maturities of Investments in Debt Securities Held (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Schedule of Available-for-sale Securities
Due within one year, cost	$ 421,024
Due after 1 year through 5 years, cost	9,325
Due after 5 years through 10 years, cost	14,026
Due after 10 years, cost	39,873
Total, cost	484,248
Due within one year, fair market value	421,088
Due after 1 year through 5 years, fair market value	9,343
Due after 5 years through 10 years, fair market value	13,659
Due after 10 years, fair maket value	40,304
Total, fair market value	$ 484,394

Schedule of Derivative Instrume

Schedule of Derivative Instruments in Statement of Financial Position at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative assets (liabilities), net	$ (274)	$ (435)
Not Designated as Hedging Instrument | Foreign currency forward contracts | Prepayments
Derivatives, Fair Value [Line Items]
Derivative assets	17	79
Not Designated as Hedging Instrument | Foreign currency forward contracts | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	$ (291)	$ (514)

Schedule of Effect of Derivativ

Schedule of Effect of Derivative Instruments in Statement of Operations Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Losses (Gains) on derivatives recognized in statements of operations	$ 3,934	$ 1,575

Schedule of Effect of Derivat_2

Schedule of Effect of Derivative Instruments in Statement of Operations Recognized (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on foreign currency transactions	$ 3.2	$ 0.6

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019	Feb. 28, 2016
Total lease expense	$ 7,200
Variable lease costs	1,400
Operating Lease, Right-of-Use Asset	50,733	$ 50,100	$ 50,100
Operating Lease, Liability	$ 55,238	$ 54,300	$ 54,300
Operating Lease, Weighted Average Remaining Lease Term	4 years 2 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	5.10%
Short-term Lease, Cost	$ 700

Supplemental Cash Flow Informat

Supplemental Cash Flow Information Related to Leases (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows	$ 5,059
Right-of-use assets obtained in exchange for new lease obligations	$ 5,737

Schedule of Operating Lease, Ma

Schedule of Operating Lease, Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Feb. 28, 2016
2019	$ 15,375
2020	18,967
2021	14,514
2022	10,262
2023	5,719
Thereafter	11,484
Total lease payments	76,321
Less imputed interest	(21,083)
Total lease liabilities	55,238	$ 54,300	$ 54,300
2019	19,570
2020	18,293
2021	13,578
2022	9,693
2023	5,449
Thereafter	9,472
Total lease payments	$ 76,055

Debt - Additional Information (

Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands, shares in Millions	Dec. 12, 2016USD ($)Customershares	Apr. 27, 2015USD ($)	Mar. 31, 2019USD ($)$ / sharesshares	Apr. 01, 2018USD ($)shares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / shares
Debt Instrument
Repurchase of common stock			$ 156,468	$ 134,276
Repurchase of stock, shares | shares			4.5	2.9
Pledge percentage of capital stock		65.00%
1.25% Convertible Senior Unsecured Notes Due December 15, 2023
Debt Instrument
Aggregate principal amount	$ 460,000		$ 460,000		$ 460,000
Debt instrument, interest rate, stated percentage	1.25%
Debt instrument, net proceeds after issuance costs	$ 450,800
Payment for net cost of convertible note hedges net of warrant proceeds	33,000
Repurchase of common stock	$ 50,100
Repurchase of stock, shares | shares	2
Senior notes maturity date	Dec. 15, 2023
Debt instrument, frequency of periodic payment	payable semiannually in arrears on June 15 and December 15 of each year
Debt instrument, date of first required payment	Jun. 15, 2017
Debt instrument, conversion option expiration date	Sep. 15, 2023
Debt instrument conversion price | $ / shares					$ 31.70	$ 31.70
Shares that would be issued upon conversion | shares					14.5
Strike price per share of warrant | $ / shares			$ 39.78
Debt instrument, convertible, carrying amount of equity component			$ 100,800			$ 100,800
Debt instrument, effective annual interest rate			5.00%
Financing cost			$ 5,100			$ 7,200
Debt issuance costs, amortization period			7 years
Unamortized discount			$ 76,400
Debt Instrument, convertible, remaining discount amortization period			4 years 8 months 12 days
Value of notes converted			$ 578,100
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 | Conversion option one
Debt Instrument
Trading days measurement period | Customer	20
Consecutive trading days measurement period | Customer	30
Percentage of conversion price	130.00%
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 | Conversion option two
Debt Instrument
Trading days measurement period | Customer	5
Consecutive trading days measurement period | Customer	5
Percentage of closing sale price of common stock and conversion rate product	98.00%
Maximum
Debt Instrument
Aggregate principal amount		$ 150,000
Commitment fee percentage of unused portion of credit facility		0.35%
Minimum
Debt Instrument
Commitment fee percentage of unused portion of credit facility		0.125%
Base Rate | Maximum
Debt Instrument
Debt instrument, basis spread on variable rate		1.00%
Base Rate | Minimum
Debt Instrument
Debt instrument, basis spread on variable rate		0.00%
London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument
Debt instrument, basis spread on variable rate		2.00%
London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument
Debt instrument, basis spread on variable rate		1.00%
Revolving Credit Facility
Debt Instrument
Financing cost			$ 2,300
Financing cost, amortization term			5 years
Revolving Credit Facility | Maximum
Debt Instrument
Credit facility, borrowing capacity		$ 350,000

Components of Convertible Senio

Components of Convertible Senior Notes (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 12, 2016
Debt Instrument
Net carrying amount of convertible debt	$ 383,590	$ 379,981
1.25% Convertible Senior Unsecured Notes Due December 15, 2023
Debt Instrument
Debt principal	460,000	460,000	$ 460,000
Unamortized discount	76,410	80,019
Net carrying amount of convertible debt	$ 383,590	$ 379,981

Interest Expense on Convertible

Interest Expense on Convertible Senior Notes (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Debt Instrument
Contractual interest expense on the coupon	$ 1,438	$ 1,438
Amortization of the discount component and debt issue fees recognized as interest expense	3,608	3,434
Total interest expense on the convertible debt	$ 5,046	$ 4,872

Schedule of Prepayments and Oth

Schedule of Prepayments and Other Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Prepaid And Other Current Assets [Line Items]
Contract manufacturer and supplier prepayments	$ 147,015	$ 131,642
Prepaid taxes	13,404	9,646
Prepaid maintenance and other services	7,703	8,487
Other prepayments	16,111	12,744
Total prepayments	$ 184,233	$ 162,519

Deferred Revenue and Customer_3

Deferred Revenue and Customer Advances (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Apr. 01, 2018	Jan. 01, 2018
Deferred Revenue Arrangement
Maintenance and training	$ 58,394	$ 58,362
Extended warranty	27,242	27,422	$ 24,590	$ 24,438
Customer advances, undelivered performance obligations and other	31,971	24,677
Total deferred revenue and customer advances	$ 117,607	$ 110,461

Warranty Accrual Included in Ot

Warranty Accrual Included in Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Product Warranty Liability [Line Items]
Balance at beginning of period	$ 7,909	$ 8,200
Acquisition	14
Accruals for warranties issued during the period	3,066	3,063
Accruals related to pre-existing warranties	1,330	(139)
Settlements made during the period	(4,567)	(3,576)
Balance at end of period	$ 7,752	$ 7,548

Extended Product Warranty of Sh

Extended Product Warranty of Short and Long-Term Deferred Revenue and Customer Advances (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Product Warranty Liability [Line Items]
Balance at beginning of period	$ 27,422	$ 24,438
Deferral of new extended warranty revenue	5,820	5,139
Recognition of extended warranty deferred revenue	(6,000)	(4,987)
Balance at end of period	$ 27,242	$ 24,590

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - $ / shares shares in Millions	1 Months Ended		3 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Mar. 31, 2019	Apr. 01, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Estimated annual dividend amount per share			$ 0.36	$ 0.36
Stock price			36.75	$ 47.70
Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award
Weighted average grant date fair value of restricted stock units granted			100,000
Weighted average grant date fair value of restricted stock units granted			$ 10.26
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Period of stock granted to employees and executive officers vest in equal annual installments			4 years
Percentage of common stock price paid			100.00%
Stock options term			7 years
Restricted Stock Units | Employees
Share-based Compensation Arrangement by Share-based Payment Award
Period of stock granted to employees and executive officers vest in equal annual installments			4 years
Restricted Stock Units | Director
Share-based Compensation Arrangement by Share-based Payment Award
Period of stock granted to employees and executive officers vest in equal annual installments			1 year
Percentage of awards vesting on the first anniversary of grant date			100.00%
TSR Performance-Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Total shareholder return performance measurement period		3 years
Minimum age of retirement to be eligible for PRSUs			60 years
Minimum years of service for retirement to be eligible for PRSUs			10 years
Restricted stock unit awards granted			0.1	0.1
Weighted average grant date fair value of restricted stock units granted			$ 48.47	$ 54.85
Stock price			36.75	47.70
TSR Performance-Based Restricted Stock Units | Measurement Input, Expected Dividend Payment [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Estimated annual dividend amount per share			$ 0.36	$ 0.36
TSR Performance-Based Restricted Stock Units | Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of vesting of target shares upon performance achieved	200.00%
TSR Performance-Based Restricted Stock Units | Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of vesting of target shares upon performance achieved	0.00%
PBIT Performance-Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Total shareholder return performance measurement period	3 years
Restricted stock unit awards granted			0.1	0.1
Weighted average grant date fair value of restricted stock units granted			$ 35.67	$ 46.62
PBIT Performance-Based Restricted Stock Units | Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of vesting of target shares upon performance achieved		200.00%
PBIT Performance-Based Restricted Stock Units | Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of vesting of target shares upon performance achieved		0.00%
Service-Based Restricted Stock Units | Employees
Share-based Compensation Arrangement by Share-based Payment Award
Restricted stock unit awards granted			0.6	0.5
Weighted average grant date fair value of restricted stock units granted			$ 46.25	$ 46.58
Service-Based Restricted Stock Units | Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award
Restricted stock unit awards granted			0.1	0.1
Weighted average grant date fair value of restricted stock units granted			$ 35.88	$ 12.17

Schedule of Estimated Fair Valu

Schedule of Estimated Fair Value of TSR Performance-Based Restricted Stock Unit Awards Assumptions (Detail) - TSR Performance-Based Restricted Stock Units	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Risk-free interest rate	2.60%	2.20%
Expected historical volatility	31.80%	26.80%
Dividend yield	1.00%	0.80%
New York Stock Exchange Composite Index
Share-based Compensation Arrangement by Share-based Payment Award
Expected historical volatility	12.00%	12.40%

Schedule of Estimated Fair Va_2

Schedule of Estimated Fair Value of Stock Options Grant Using Black Scholes Option Pricing Model (Detail) - Stock Options	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Expected life (years)	5 years	5 years
Risk-free interest rate	2.60%	2.40%
Volatility-historical	30.10%	26.40%
Dividend yield	1.00%	0.80%

Changes in Accumulated Other Co

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.”

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss), tax	$ (31)	$ 60
Other comprehensive income (loss), tax	11	18
Reclassification of income tax effects from the Tax Reform Act, net of tax		769
Reclassification of unrealized gains on equity securities, net of tax	(20)	(78)
Foreign currency translation adjustments, tax	0	0	$ 0	$ 0
Unrealized (losses) gains on marketable securities, tax	36	418	521	1,815
Retirement plans prior service benefit, tax	1,092	1,028	$ 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
Reclassification of unrealized gains on equity securities, net of tax		0
Unrealized (Losses) Gains on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, tax	577	718
Amounts reclassified from accumulated other comprehensive income (loss), tax	20	78
Other comprehensive income (loss), tax	557	640
Reclassification of income tax effects from the Tax Reform Act, net of tax		691
Reclassification of unrealized gains on equity securities, net of tax		(902)
Unrealized (losses) gains on marketable securities, tax	20	78
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	11	18
Other comprehensive income (loss), tax	$ 11	18
Reclassification of income tax effects from the Tax Reform Act, net of tax		78
Reclassification of unrealized gains on equity securities, net of tax		$ 0

Reclassifications Out of Accumu

Reclassifications Out of Accumulated Other Comprehensive Income to Statements of Operations (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Apr. 01, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income and interest expense		$ (8,052)	$ (5,981)
Reclassifications, net of tax		107	0
Unrealized Gains (Losses) on Marketable Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax		70	(1,668)
Amortization of Prior Service Credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax	[1]	37	61
Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax		107	769
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Marketable Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income and interest expense		$ 70	$ (1,668)
[1]	The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit. See Note R: “Retirement Plans.”

Reclassifications Out of Accu_2

Reclassifications Out of Accumulated Other Comprehensive Income to Statements of Operations (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, tax	$ 31	$ (60)
Unrealized (Losses) Gains on Marketable Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, tax	(20)	(78)
Amortization of Prior Service Credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, tax	$ (11)	$ (18)

Goodwill and Acquired Intangi_3

Goodwill and Acquired Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Line Items]
Acquired intangible assets amortization	$ 10,634	$ 7,698	$ 7,700

Changes in Carrying Amount of G

Changes in Carrying Amount of Goodwill by Segment (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019
Goodwill [Line Items]
Goodwill acquisition	$ 1,145
Foreign currency translation adjustment	(3,482)
Goodwill	1,144,416	$ 1,142,079
Accumulated impairment losses	(762,566)	(762,566)
Goodwill	381,850,000	379,513,000
Industrial Automation
Goodwill [Line Items]
Foreign currency translation adjustment	(3,494)
Goodwill	363,358	359,864
Goodwill	363,358	359,864
Wireless Test
Goodwill [Line Items]
Goodwill	361,819	361,819
Accumulated impairment losses	(353,843)	(353,843)
Goodwill	7,976	7,976
Semiconductor Test
Goodwill [Line Items]
Goodwill acquisition	1,145
Foreign currency translation adjustment	12
Goodwill	260,540	261,697
Accumulated impairment losses	(260,540)	(260,540)
Goodwill		1,157
System Test
Goodwill [Line Items]
Goodwill	158,699	158,699
Accumulated impairment losses	(148,183)	(148,183)
Goodwill	$ 10,516	$ 10,516

Schedule of Amortizable Intangi

Schedule of Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets
Gross Carrying Amount	[1]	$ 503,731	$ 498,231
Accumulated Amortization		(378,164)	(367,531)
Foreign Currency Translation Adjustment		(6,195)	(5,218)
Net Carrying Amount		119,372	125,482
Developed technology
Finite-Lived Intangible Assets
Gross Carrying Amount	[1]	337,218	336,308
Accumulated Amortization		(259,129)	(252,080)
Foreign Currency Translation Adjustment		(4,812)	(4,079)
Net Carrying Amount		73,277	80,149
Customer Relationships
Finite-Lived Intangible Assets
Gross Carrying Amount	[1]	100,743	97,153
Accumulated Amortization		(85,469)	(83,448)
Foreign Currency Translation Adjustment		(408)	(340)
Net Carrying Amount		14,866	13,365
Trademarks and tradenames
Finite-Lived Intangible Assets
Gross Carrying Amount	[1]	64,670	64,420
Accumulated Amortization		(32,897)	(31,653)
Foreign Currency Translation Adjustment		(973)	(799)
Net Carrying Amount		30,800	31,968
Non-compete Agreements
Finite-Lived Intangible Assets
Gross Carrying Amount	[1]	320	320
Accumulated Amortization			(320)
Backlog
Finite-Lived Intangible Assets
Gross Carrying Amount	[1]	780	30
Accumulated Amortization		(349)	$ (30)
Foreign Currency Translation Adjustment		(2)
Net Carrying Amount		$ 429
[1]	Includes $5.5 million of intangible assets from Lemsys acquisition.

Schedule of Amortizable Intan_2

Schedule of Amortizable Intangible Assets (Parenthetical) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Lemsys [Member]
Finite-Lived Intangible Assets
Intangible assets acquired	$ 5.5

Schedule of Estimated Intangibl

Schedule of Estimated Intangible Asset Amortization Expense (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Finite-Lived Intangible Assets
2019 (remainder)	$ 29,184
2020	24,852
2021	14,707
2022	13,815
2023	13,339
Thereafter	$ 23,475

Computation of Basic and Dilute

Computation of Basic and Diluted Net (Loss) Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2019	Apr. 01, 2018
Net Income Loss Per Common Share
Net income for basic and diluted net income per share		$ 109,138	$ 86,974
Weighted average common shares-basic		173,532	195,255
Incremental shares from assumed conversion of convertible notes	[1]	2,186	4,398
Convertible note hedge warrant shares	[2]		1,830
Employee stock purchase plan		11	14
Dilutive potential common shares		3,440	8,229
Weighted average common shares-diluted		176,972	203,484
Net income per common share-basic		$ 0.63	$ 0.45
Net income per common share-diluted		$ 0.62	$ 0.43
Restricted Stock Units
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		1,021	1,666
Stock Options
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		222	321
[1]	Incremental shares from assumed conversion of the convertible notes was calculated using the difference between the average Teradyne stock price for the period and the conversion price of $31.70, multiplied by 14.5 million shares. The result of this calculation, representing the total intrinsic value of the convertible debt, was divided by the average Teradyne stock price for the period.
[2]	Convertible notes hedge warrant shares were calculated using the difference between the average Teradyne stock price for the period and the warrant price of $39.78, multiplied by 14.5 million shares. The result of this calculation, representing the total intrinsic value of the warrant, was divided by the average Teradyne stock price for the period.

Computation of Basic and Dilu_2

Computation of Basic and Diluted Net (Loss) Income Per Common Share (Parenthetical) (Detail) shares in Millions	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Convertible Notes
Net Income Loss Per Common Share
Initial debt conversion price | $ / shares	$ 31.70
Shares that would be issued upon conversion | shares	14.5
Convertible Notes Hedge Warrant
Net Income Loss Per Common Share
Initial debt conversion price | $ / shares	$ 39.78
Shares that would be issued upon conversion | shares	14.5

Net Income Per Common Share - A

Net Income Per Common Share - Additional Information (Detail) - shares shares in Millions	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Restricted Stock Units (RSUs) [Member]
Net Income Loss Per Common Share
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0.6	0.4

Restructuring and Other - Addit

Restructuring and Other - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Restructuring Cost and Reserve
Contingent consideration adjustment	$ 2,970	$ (4,968)
Severance benefit and charges		3,900
Acquisition related costs	1,300	800
Universal Robots (UR)
Restructuring Cost and Reserve
Contingent consideration adjustment	3,000	$ 5,000
Mobile Industrial Robots (MiR)
Restructuring Cost and Reserve
Contingent consideration adjustment	800
System Test and Semiconductor Test
Restructuring Cost and Reserve
Severance benefit and charges	$ 3,000

Retirement Plans - Additional I

Retirement Plans - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
United States Plans
Defined Benefit Plan Disclosure
Contribution to defined benefit pension plans	$ 0.7
U.S. Supplemental Executive Defined Benefit Pension Plan
Defined Benefit Plan Disclosure
Contribution to defined benefit pension plans	$ 0.2

Schedule of Net Periodic Pensio

Schedule of Net Periodic Pension and Postretirement (income) Cost (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
UNITED STATES
Defined Benefit Plan Disclosure
Service cost	$ 405	$ 571
Interest cost	1,795	2,997
Expected return on plan assets	(1,511)	(3,369)
Amortization of prior service cost		14
Total net periodic pension cost	689	213
Foreign Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Service cost	188	213
Interest cost	173	186
Expected return on plan assets	(7)	(5)
Total net periodic pension cost	354	394
Postretirement Benefit Plans
Defined Benefit Plan Disclosure
Service cost	9	9
Interest cost	85	50
Amortization of prior service cost	(48)	(93)
Special termination benefits		1,626
Total net periodic pension cost	$ 46	$ 1,592

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	Mar. 31, 2019USD ($)
Purchase Commitment, Excluding Long-term Commitment
Aggregate purchase commitments	$ 263
Purchase commitments less than one year	$ 255.3

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Dec. 31, 2018
Income Taxes [Line Items]
Effective tax rate	(16.10%)	9.20%
Expense related to remeasurement of deferred tax assets and liabilities		$ 1.7
Tax savings due to the tax holiday	$ 2.1	$ 3
Tax savings due to the tax holiday, per share	$ 0.01	$ 0.01
Reduction in un recognized tax benefits	$ 22.4
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0.2
Accrued interest and penalties	0.6		$ 0.3
Interest and penalties related to income tax, expense (benefit)	0.3	$ 0.1
Discrete tax benefits	30.2	6
Discrete tax benefit, Other		0.7
Discrete tax benefits, stock based compensation	3.8	7.6
Discrete tax benefits, net	30.2	6
Income Tax Reconciliation Tax Contingencies Other Tax Expense	0.5	$ 0.6
Uncertain tax positions	13.5		$ 43.4
Net decrease in uncertain tax positions	29.9
Release of Tax Reserve Discrete Tax Credit	28.8
Research Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Net decrease in uncertain tax positions	7.4
United States
Income Taxes [Line Items]
Discrete tax expense	2.9
Net decrease in uncertain tax positions	$ 22.4

Segment Information - Additiona

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019Segment
Segment Reporting Information [Line Items]
Number of Operating Segments	4

Schedule of Segment Information

Schedule of Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019		Apr. 01, 2018		Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues		$ 494,099		$ 487,467
Income (loss) before income taxes	[1],[2]	93,979		95,820
Total assets		2,616,643	[3]	2,995,193	[3]	$ 2,706,606
Semiconductor Test
Segment Reporting Information [Line Items]
Revenues		340,853		373,328
Income (loss) before income taxes	[1],[2]	83,049		88,079
Total assets	[3]	770,967		758,737
System Test
Segment Reporting Information [Line Items]
Revenues		58,220		43,019
Income (loss) before income taxes	[1],[2]	15,340		5,888
Total assets	[3]	98,916		90,785
Industrial Automation
Segment Reporting Information [Line Items]
Revenues		66,136		48,834
Income (loss) before income taxes	[1],[2]	5,295		784
Total assets	[3]	596,899		406,557
Wireless Test
Segment Reporting Information [Line Items]
Revenues		29,041		22,507
Income (loss) before income taxes	[1],[2]	3,628		464
Total assets	[3]	73,066		59,739
Corporate And Others [Member]
Segment Reporting Information [Line Items]
Revenues		(151)		(221)
Income (loss) before income taxes	[1],[2]	2,743		605
Total assets	[3]	$ 1,076,795		$ 1,679,375
[1]	Included in Corporate and Other are: contingent consideration adjustments, severance charges, interest income, interest expense, net foreign exchange gains (losses), intercompany eliminations and acquisition related charges.
[2]	Included in the income (loss) before income taxes for each of the segments are charges and credits related to restructuring and other and inventory charges.
[3]	Total business assets are directly attributable to each business. Corporate assets consist of cash and cash equivalents, marketable securities and certain other assets.

Schedule of Segment Reporting I

Schedule of Segment Reporting Information by Segment Charges (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Segment Reporting Information [Line Items]
Acquisition related costs	$ 1,300	$ 800
Restructuring and other-employee severance	5,112	(313)
Contingent consideration adjustment	2,970	(4,968)
Universal Robots (UR)
Segment Reporting Information [Line Items]
Contingent consideration adjustment	3,000	5,000
Mobile Industrial Robots (MiR)
Segment Reporting Information [Line Items]
Contingent consideration adjustment	800
Semiconductor Test
Segment Reporting Information [Line Items]
Cost of revenues-inventory charge	1,174	2,166
Semiconductor Test | Severance And Benefits
Segment Reporting Information [Line Items]
Restructuring and other-employee severance	567	3,761
System Test
Segment Reporting Information [Line Items]
Cost of revenues-inventory charge	468	320
Industrial Automation
Segment Reporting Information [Line Items]
Acquisition related costs	1,261
Cost of revenues-inventory charge	416	200
Wireless Test
Segment Reporting Information [Line Items]
Cost of revenues-inventory charge	339	836
Corporate And Eliminations | Restructuring and other
Segment Reporting Information [Line Items]
Acquisition related costs		774
Corporate And Eliminations | Universal Robots (UR) | Restructuring and other
Segment Reporting Information [Line Items]
Contingent consideration adjustment		$ (4,968)
Corporate And Eliminations | Mobile Industrial Robots (MiR) | Restructuring and other
Segment Reporting Information [Line Items]
Contingent consideration adjustment	$ 3,003

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Dec. 31, 2019	Jan. 31, 2019	Jan. 31, 2018
Cumulative repurchases, value	$ 151,470	$ 140,672
Cumulative repurchases, shares	4.5	2.9
Common stock average price	$ 35.12	$ 45.69
Dividends Payable, Amount Per Share				$ 0.09	$ 0.09
Dividend payment	$ 15,627	$ 17,588
Share Repurchase Program [Member]
Stock repurchase program, authorized amount	26,100
Cumulative repurchases, value	$ 979,900
Common stock average price	$ 37.55
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	1.5
Maximum [Member]
Stock repurchase program, authorized amount					$ 1,500,000
Scenario, Forecast [Member]
Cumulative repurchases, value			$ 500,000