Teradyne (TER) 10-Q 7 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 28, 2014	Oct. 31, 2014
Document Information	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	28-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'TER	'
Entity Registrant Name	'TERADYNE, INC	'
Entity Central Index Key	'0000097210	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	216,494,252

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$211,704	$341,638
Marketable securities	594,801	586,882
Accounts receivable, less allowance for doubtful accounts of $2,438 and $2,912 at September 28, 2014 and December 31, 2013, respectively	321,312	157,642
Inventories:	'	'
Parts	64,588	84,232
Assemblies in process	11,147	15,539
Finished goods	32,642	38,168
Inventory, Net, Total	108,377	137,939
Deferred tax assets	68,791	72,478
Prepayments	88,732	136,374
Other current assets	7,304	7,324
Total current assets	1,401,021	1,440,277
Net property, plant and equipment	335,805	275,236
Marketable securities	374,808	271,078
Deferred tax assets	5,353	5,217
Other assets	9,853	14,591
Retirement plans assets	8,871	9,342
Intangible assets, net	197,477	252,291
Goodwill	361,819	361,792
Total assets	2,695,007	2,629,824
Current liabilities:	'	'
Accounts payable	60,309	62,874
Accrued employees' compensation and withholdings	91,053	95,619
Deferred revenue and customer advances	60,178	55,404
Other accrued liabilities	98,424	63,712
Accrued income taxes	19,840	11,360
Current debt	'	186,663
Total current liabilities	329,804	475,632
Long-term deferred revenue and customer advances	23,248	13,756
Retirement plans liabilities	88,670	91,517
Deferred tax liabilities	35,911	40,686
Long-term other accrued liabilities	27,466	23,139
Total liabilities	505,099	644,730
Commitments and contingencies (Note O)	'	'
SHAREHOLDERS' EQUITY	'	'
Common stock, $0.125 par value, 1,000,000 shares authorized, 216,482 shares and 191,731 shares issued and outstanding at September 28, 2014 and December 31, 2013, respectively	27,060	23,966
Additional paid-in capital	1,431,100	1,390,896
Accumulated other comprehensive income	4,859	4,000
Retained earnings	726,889	566,232
Total shareholders' equity	2,189,908	1,985,094
Total liabilities and shareholders' equity	$2,695,007	$2,629,824

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, except Per Share data, unless otherwise specified
Accounts receivable, less allowance for doubtful accounts	$2,438	$2,912
Common stock, par value	$0.13	$0.13
Common stock, shares authorized	1,000,000	1,000,000
Common stock, shares issued	216,482	191,731
Common stock, shares outstanding	216,482	191,731

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations (USD $)	3 Months Ended				9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 28, 2014		Sep. 29, 2013		Sep. 28, 2014		Sep. 29, 2013
Net revenues:	'		'		'		'
Products	$402,987		$365,825		$1,110,861		$943,212
Services	75,023		67,551		213,726		199,420
Total net revenues	478,010		433,376		1,324,587		1,142,632
Cost of revenues:	'		'		'		'
Cost of products	182,591		150,365		509,450		405,569
Cost of services	34,298		28,717		96,556		88,119
Total cost of revenues (exclusive of acquired intangible assets amortization shown separately below)	216,889		179,082		606,006		493,688
Gross profit	261,121		254,294		718,581		648,944
Operating expenses:	'		'		'		'
Engineering and development	71,953		68,918		212,452		199,442
Selling and administrative	73,064		72,917		228,556		210,037
Acquired intangible assets amortization	18,271		18,064		54,813		54,163
Restructuring and other	-405		889		167		1,480
Total operating expenses	162,883		160,788		495,988		465,122
Income from operations	98,238		93,506		222,593		183,822
Interest income	1,922		948		4,224		2,923
Interest expense and other (income) expense	-510		6,902		6,628		20,262
Income before income taxes	100,670	[1],[2]	87,552	[1],[2]	220,189	[1],[2]	166,483	[1],[2]
Income tax provision	17,721		18,093		35,106		23,879
Net income	$82,949		$69,459		$185,083		$142,604
Net income per common share:	'		'		'		'
Basic	$0.40		$0.36		$0.93		$0.75
Diluted	$0.38		$0.29		$0.83		$0.61
Weighted average common shares-basic	207,381		191,307		198,367		190,521
Weighted average common shares-diluted	218,333		235,828		223,795		235,165
Cash dividend declared per common share	$0.06		'		$0.12		'
[1]	Pension and postretirement actuarial gains and losses, interest income, and interest expense and other are included in Corporate and Eliminations.
[2]	Included in the income (loss) before income taxes for each of the segments are charges and credits for the three and nine months ended September 28, 2014 and September 29, 2013 that include restructuring and other, and provision for excess and obsolete inventory, as follows:

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014		Sep. 29, 2013		Sep. 28, 2014		Sep. 29, 2013
Net income	$82,949		$69,459		$185,083		$142,604
Other comprehensive income (loss):	'		'		'		'
Net unrealized gains (losses) on marketable securities arising during period, net of tax (benefit) expense of $(139), $358, $1,103, $(367)	-138		623		2,166		-640
Less: Reclassification adjustment for net gains included in net income, net of tax (benefit) of $(348), $(109), $(591), $(231)	-638		-189		-1,086		-401
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Total	-776		434		1,080		-1,041
Defined benefit pension and post-retirement plans:	'		'		'		'
Amortization of net prior service benefit included in net periodic pension expense and post-retirement income, net of tax (benefit) of $(42), $(40), $(127), $(119)	-74	[1]	-69	[1]	-221	[1]	-207	[1]
Other comprehensive income (loss)	-850		365		859		-1,248
Comprehensive income	$82,099		$69,824		$185,942		$141,356
[1]	The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit; see Note N: "Retirement Plans."

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Net unrealized gains on marketable securities arising during period, tax (benefit) expense	($139)	$358	$1,103	($367)
Reclassification adjustment for net gains included in net income, tax (benefit)	-348	-109	-591	-231
Amortization of prior service benefit, tax (benefit)	($42)	($40)	($127)	($119)

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013
Cash flows from operating activities:	'	'
Net income	$185,083	$142,604
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation	52,832	41,873
Amortization	62,122	69,495
Stock-based compensation	31,873	27,227
Provision for excess and obsolete inventory	21,505	9,616
Deferred taxes	-8,747	-19,211
Contingent consideration fair value adjustment	-630	'
Tax benefit related to stock options and restricted stock units	-1,726	-807
Retirement plans actuarial gains	'	-1,359
Impairment loss on property, plant and equipment	'	1,074
Other	2,110	1,088
Changes in operating assets and liabilities:	'	'
Accounts receivable	-163,670	-55,963
Inventories	38,267	34,194
Prepayments and other assets	47,784	-26,312
Accounts payable and other accrued expenses	29,109	-17
Deferred revenue and customer advances	14,266	-9,249
Retirement plans contributions	-3,281	-3,569
Accrued income taxes	10,208	13,750
Net cash provided by operating activities	317,105	224,434
Cash flows from investing activities:	'	'
Purchases of property, plant and equipment	-146,352	-82,925
Purchases of marketable securities	-844,056	-658,564
Proceeds from maturities of marketable securities	495,565	401,901
Proceeds from sales of marketable securities	236,060	332,968
Proceeds from life insurance	4,391	'
Net cash used for investing activities	-254,392	-6,620
Cash flows from financing activities:	'	'
Issuance of common stock under employee stock purchase and stock options plans	21,030	16,778
Tax benefit related to stock options and restricted stock units	1,726	807
Payments of dividend	-24,428	'
Payments of long-term debt	-190,975	-1,063
Payments of contingent consideration	'	-388
Net cash (used for) provided by financing activities	-192,647	16,134
(Decrease) increase in cash and cash equivalents	-129,934	233,948
Cash and cash equivalents at beginning of period	341,638	338,920
Cash and cash equivalents at end of period	$211,704	$572,868

The_Company

The Company	9 Months Ended
	Sep. 28, 2014
The Company	'
	A. The Company
	Teradyne, Inc. (the “Company” or “Teradyne”) is a leading global supplier of automatic test equipment. Teradyne’s automatic test equipment products and services include:
		•	semiconductor test (“Semiconductor Test”) systems;
		•	wireless test (“Wireless Test”) systems; and
		•	military/aerospace (“Mil/Aero”) test instrumentation and systems, storage test (“Storage Test”) systems, and circuit-board test (“Production Board Test”) systems (collectively these products represent “System Test”).

Accounting_Policies

Accounting Policies	9 Months Ended
	Sep. 28, 2014
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 presentation of such interim financial statements. Certain prior year’s amounts were reclassified to conform to the current year presentation. The December 31, 2013 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 February 28, 2014, for the year ended December 31, 2013.
	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.

Recently_Issued_Accounting_Pro

Recently Issued Accounting Pronouncements	9 Months Ended
	Sep. 28, 2014
Recently Issued Accounting Pronouncements	'
	C. Recently Issued Accounting Pronouncements
	On July 18, 2013, Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2013-11, “Income Taxes (Topic 740): Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists.” Under this ASU, unrecognized tax benefits will be netted against all available same-jurisdiction loss or other tax carryforwards that would be utilized, rather than only against carryforwards that are created by unrecognized tax benefits. The provisions of this ASU are effective for interim and annual periods beginning on or after December 15, 2013. Teradyne’s implementation of this ASU did not have a material impact on Teradyne’s financial position and results of operations.
	In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” which will replace numerous requirements in U.S. GAAP, including industry-specific requirements, and provide companies with a single revenue recognition model for recognizing revenue from contracts with customers. The core principle of the new standard is that a company should recognize revenue to show the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The new standard will be effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. For Teradyne, the standard will be effective in the first quarter of 2017. The two permitted transition methods under the new standard are the full retrospective method, in which case the standard would be applied to each prior reporting period presented, or the modified retrospective method, in which case the cumulative effect of applying the standard would be recognized at the date of initial application. Teradyne has not yet selected a transition method. Teradyne is currently evaluating the impact of this ASU on its financial position and results of operations.

Financial_Instruments_and_Deri

Financial Instruments and Derivatives	9 Months Ended
	Sep. 28, 2014
Financial Instruments and Derivatives	'
	D. Financial Instruments and Derivatives
	Cash Equivalents
	Teradyne considers all highly liquid investments with maturities of three months or less at the date of acquisition to be cash equivalents.
	Financial Instruments
	Teradyne accounts for its investments in debt and equity securities in accordance with the provisions of ASC 320-10, “Investments—Debt and Equity Securities.” ASC 320-10 requires that certain debt and equity securities be classified into one of three categories; trading, available-for-sale or held-to-maturity securities. As of September 28, 2014, Teradyne’s investments in debt and equity securities were classified as available-for-sale and recorded at their fair market value.
	On a quarterly basis, Teradyne reviews its investments to identify and evaluate those that have an indication of a potential other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include:
		•		The length of time and the extent to which the market value has been less than cost;
		•		The financial condition and near-term prospects of the issuer; and
		•		The intent and ability to retain the investment in the issuer for a period of time sufficient to allow for any anticipated recovery in market value.
	Teradyne uses the market and income approach techniques to value its financial instruments and there were no changes in valuation techniques during the three and nine months ended September 28, 2014 and September 29, 2013. As defined in ASC 820-10 “Fair Value Measurements and Disclosures”, fair value is the price that would be received from the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. ASC 820-10 requires that assets and liabilities carried at fair value be classified and disclosed in one of the following three categories:
	Level 1: Quoted prices in active markets for identical assets as of the reporting date.
	Level 2: Inputs other than Level 1, that are observable either directly or indirectly as of the reporting date. For example, a common approach for valuing fixed income securities is the use of matrix pricing, a technique used to value securities by relying on the securities’ relationship to other benchmark quoted prices, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.
	Level 3: Unobservable inputs that are not supported by market data. Unobservable inputs are developed based on the best information available, which might include Teradyne’s own data.
	Substantially all of Teradyne’s fixed income securities are classified as Level 2, with the exception of investments in equity and debt mutual funds, which are classified as Level 1, and contingent consideration, which is classified as Level 3. The majority of Teradyne’s Level 2 securities are priced by 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 nine months ended September 28, 2014 and September 29, 2013, there were no transfers in or out of Level 1, Level 2 or Level 3 financial instruments.
	Realized gains and (losses) for the three and nine months ended September 28, 2014 and September 29, 2013 were as follows:
			For the Three Months								For the Nine Months
			Ended								Ended
			September 28,				September 29,				September 28,			September 29,
			2014				2013				2014			2013
			(in thousands)
	Realized gains		$	986			$	235			$	1,677		$	569
	Realized (losses)			—				—				—			—
	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 September 28, 2014 and December 31, 2013.
			September 28, 2014
			Quoted Prices				Significant				Significant			Total
			in Active				Other				Unobservable
			Markets for				Observable				Inputs
			Identical				Inputs				(Level 3)
			Instruments				(Level 2)
			(Level 1)
			(in thousands)
	Assets
	Cash		$	100,633			$	—			$	—		$	100,633
	Cash equivalents			99,979				11,092				—			111,071
	Available-for-sale securities:
	U.S. Treasury securities			—				459,240				—			459,240
	U.S. government agency securities			—				285,617				—			285,617
	Commercial paper			—				99,774				—			99,774
	Corporate debt securities			—				94,357				—			94,357
	Certificates of deposit and time deposits			—				18,522				—			18,522
	Equity and debt mutual funds			12,099				—				—			12,099
	Total		$	212,711			$	968,602			$	—		$	1,181,313
	Liabilities
	Contingent consideration		$	—			$	—			$	1,600		$	1,600
	Derivatives			—				546				—			546
	Total		$	—			$	546			$	1,600		$	2,146
	Reported as follows:
			(Level 1)				(Level 2)				(Level 3)			Total
			(in thousands)
	Assets
	Cash and cash equivalents		$	200,612			$	11,092			$	—		$	211,704
	Marketable securities			—				594,801				—			594,801
	Long-term marketable securities			12,099				362,709				—			374,808
			$	212,711			$	968,602			$	—		$	1,181,313
	Liabilities
	Other accrued liabilities		$	—			$	546			$	—		$	546
	Long-term other accrued liabilities			—				—				1,600			1,600
			$	—			$	546			$	1,600		$	2,146
			December 31, 2013
			Quoted Prices				Significant				Significant			Total
			in Active				Other				Unobservable
			Markets for				Observable				Inputs
Identical			Inputs				(Level 3)
Instruments			(Level 2)
(Level 1)
		(in thousands)
Assets
Cash		$	117,242			$	—			$	—		$	117,242
Cash equivalents			165,865				58,531				—			224,396
Available-for-sale securities:
U.S. Treasury securities			—				467,895				—			467,895
U.S. government agency securities			—				202,588				—			202,588
Commercial paper			—				105,598				—			105,598
Corporate debt securities			—				65,387				—			65,387
Equity and debt mutual funds			13,156				—				—			13,156
Certificates of deposit and time deposits			—				3,258				—			3,258
Non-U.S. government securities			—				78				—			78
Total			296,263				903,335				—			1,199,598
Derivatives			—				153				—			153
Total		$	296,263			$	903,488			$	—		$	1,199,751
Liabilities
Contingent consideration		$	—			$	—			$	2,230		$	2,230
Total		$	—			$	—			$	2,230		$	2,230
Reported as follows:
		(Level 1)				(Level 2)				(Level 3)			Total
		(in thousands)
Assets
Cash and cash equivalents		$	283,107			$	58,531			$	—		$	341,638
Marketable securities			—				586,882				—			586,882
Long-term marketable securities			13,156				257,922				—			271,078
Other current assets			—				153				—			153
		$	296,263			$	903,488			$	—		$	1,199,751
Liabilities
Long-term other accrued liabilities		$	—			$	—			$	2,230		$	2,230
		$	—			$	—			$	2,230		$	2,230
Contingent consideration relates to Teradyne’s acquisition of ZTEC Instruments, Inc. (“ZTEC”) on October 25, 2013. The total purchase price included $2.2 million in fair value of contingent consideration payable upon achievement of certain customer order and revenue targets through 2015. The maximum amount of contingent consideration that could be paid is $5.0 million. Based on the projected results for the acquisition, no value was assigned to the revenue component of the contingent consideration.
The acquisition date valuation of the customer order component of the contingent consideration utilized the following assumptions: (1) probability of meeting each benchmark; (2) expected timing of meeting each benchmark; and (3) discount rate reflecting the risk associated with the expected payments. The probabilities and timing for each benchmark were estimated based on a review of the historical and projected results. A discount rate of 5.2 percent was selected based on the cost of debt for the business, as a significant portion of the risk in achieving the customer order contingent consideration was captured in the probabilities assigned to meeting each benchmark. Teradyne assesses these assumptions and estimates on a quarterly basis as additional data impacting the assumptions is obtained. During the three and nine months ended September 28, 2014, the fair value of the customer order component of the contingent consideration was reduced by $0.6 million based on updated assumptions and estimates. The fair value reduction was recorded as a gain in restructuring and other in the statement of operations.
Changes in the fair value of Level 3 contingent consideration for the three and nine months ended September 28, 2014 and September 29, 2013 were as follows:
Contingent consideration related to Teradyne’s acquisition of ZTEC		For the Three and Nine Months
in October 2013		Ended
		28-Sep-14
		(in thousands)
Balance at December 31, 2013		$	2,230
Contingent consideration payments			—
Balance at March 30, 2014			2,230
Contingent consideration payments			—
Balance at June 29, 2014			2,230
Fair value adjustment			(630	)
Balance at September 28, 2014		$	1,600
Contingent consideration related to Teradyne’s acquisition of LitePoint		For the Three and Nine Months
in October 2011		Ended
		29-Sep-13
		(in thousands)
Balance at December 31, 2012		$	388
Contingent consideration payments			(313	)
Balance at March 31, 2013			75
Contingent consideration payments			(75	)
Balance at June 30, 2013			—
Contingent consideration payments			—
Balance at September 29, 2013		$	—
The carrying amounts and fair values of Teradyne’s financial instruments at September 28, 2014 and December 31, 2013 were as follows:
		September 28, 2014								December 31, 2013
		Carrying Value				Fair Value				Carrying Value			Fair Value
		(in thousands)
Cash and cash equivalents		$	211,704			$	211,704			$	341,638		$	341,638
Marketable securities			969,609				969,609				857,960			857,960
Convertible debt(1)			—				—				185,708			611,433
Japan loan			—				—				955			955
-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 feature.
The fair values of cash and cash equivalents, accounts receivable, net and accounts payable approximate the carrying amount due to the short-term nature of these instruments.
The following tables summarize the composition of available-for-sale marketable securities at September 28, 2014 and December 31, 2013:
		September 28, 2014
		Available-for-Sale														Fair Market
																Value of
																Investments
																with Unrealized
		Cost				Unrealized				Unrealized			Fair Market			Losses
						Gain				(Loss)			Value
		(in thousands)
U.S. Treasury securities		$	458,958			$	373			$	(91	)	$	459,240		$	64,267
U.S. government agency securities			285,528				195				(106	)		285,617			66,700
Commercial paper			99,767				11				(4	)		99,774			23,722
Corporate debt securities			92,883				1,734				(260	)		94,357			56,393
Certificates of deposit and time deposits			18,508				14				—			18,522			—
Equity and debt mutual funds			10,199				1,933				(33	)		12,099			1,074
		$	965,843			$	4,260			$	(494	)	$	969,609		$	212,156
Reported as follows:
		Cost				Unrealized				Unrealized			Fair Market			Fair Market
						Gain				(Loss)			Value			Value of
																Investments
																with Unrealized
																Losses
		(in thousands)
Marketable securities		$	594,500			$	319			$	(18	)	$	594,801		$	66,188
Long-term marketable securities			371,343				3,941				(476	)		374,808			145,968
		$	965,843			$	4,260			$	(494	)	$	969,609		$	212,156
		December 31, 2013
		Available-for-Sale														Fair Market
																Value of
																Investments
																with Unrealized
		Cost				Unrealized				Unrealized			Fair Market			Losses
						Gain				(Loss)			Value
		(in thousands)
U.S. Treasury securities		$	468,084			$	94			$	(283	)	$	467,895		$	108,212
U.S. government agency securities			202,573				75				(60	)		202,588			84,498
Commercial paper			105,583				16				(1	)		105,598			7,993
Corporate debt securities			65,747				762				(1,122	)		65,387			40,355
Equity and debt mutual funds			10,463				2,742				(49	)		13,156			702
Certificates of deposit and time deposits			3,258				—				—			3,258			—
Non-U.S. government securities			78				—				—			78			—
		$	855,786			$	3,689			$	(1,515	)	$	857,960		$	241,760
Reported as follows:
		Cost				Unrealized				Unrealized			Fair Market			Fair Market
						Gain				(Loss)			Value			Value of
																Investments
																with Unrealized
																Losses
		(in thousands)
Marketable securities		$	586,818			$	85			$	(21	)	$	586,882		$	137,670
Long-term marketable securities			268,968				3,604				(1,494	)		271,078			104,090
		$	855,786			$	3,689			$	(1,515	)	$	857,960		$	241,760
As of September 28, 2014, the fair market value of investments with unrealized losses was $212.2 million. Of this value, $5.0 million had unrealized losses greater than one year and $207.2 million had unrealized losses less than one year. As of December 31, 2013, the fair market value of investments with unrealized losses was $241.8 million. Of this value, $0.9 million had unrealized losses greater than one year and $240.9 million had unrealized losses 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 September 28, 2014 and December 31, 2013, were temporary.
The contractual maturities of investments held at September 28, 2014 were as follows:
		September 28, 2014
		Cost				Fair Market
						Value
		(in thousands)
Due within one year		$	594,500			$	594,801
Due after 1 year through 5 years			330,340				330,412
Due after 5 years through 10 years			5,772				5,859
Due after 10 years			25,032				26,438
Total		$	955,644			$	957,510
Contractual maturities of investments held at September 28, 2014 exclude equity and 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 the monetary assets and liabilities denominated in foreign currencies.
The notional amount of foreign currency forward contracts was $67.9 million and $74.8 million at September 28, 2014 and December 31, 2013, respectively.
The fair value of the outstanding contracts was a loss of $0.6 million and a gain of $0.2 million at September 28, 2014 and December 31, 2013, respectively. The following table summarizes the fair value of derivative instruments at September 28, 2014 and December 31, 2013:
		Balance Sheet Location		September 28,				December 31,
				2014				2013
				(in thousands)
Derivatives not designated as hedging instruments:
Foreign currency forward contracts		Other current assets		$	—			$	153
		Other accrued liabilities			546				—
				$	546			$	153
Teradyne had no offsetting foreign exchange contracts at September 28, 2014 and December 31, 2013.
In the three and nine months ended September 28, 2014, Teradyne recorded net realized gains (losses) of $0.2 million and $(1.6) million, respectively, related to foreign currency forward contracts hedging net monetary positions. In the three and nine months ended September 29, 2013, Teradyne recorded net realized gains of $0.0 million and $4.1 million, respectively, related to foreign currency forward contracts hedging net monetary positions. Gains and losses on foreign currency forward contracts and foreign currency remeasurement gains and losses on monetary assets and liabilities are included in interest expense and other.
The following table summarizes the effect of derivative instruments recognized in the statement of operations during the three and nine months ended September 28, 2014 and September 29, 2013. The table does not reflect the corresponding gains (losses) from the remeasurement of the monetary assets and liabilities denominated in foreign currencies. For the three and nine months ended September 28, 2014, (losses) gains from the remeasurement of the monetary assets and liabilities denominated in foreign currencies were $(0.4) million and $0.9 million, respectively. For the three and nine months ended September 29, 2013, losses from the remeasurement of the monetary assets and liabilities denominated in foreign currencies were $(0.4) million and $(5.0) million, respectively.
		Location of Gains				For the Three Months							For the Nine Months
		(Losses)				Ended							Ended
		Recognized in
		Statement
		of Operations				September 28,				September 29,			September 28,			September 29,
						2014				2013			2014			2013
						(in thousands)
Derivatives not designated as hedging instruments:
Foreign exchange contracts			Interest expense and other			$	237			$	—		$	(1,632	)	$	4,068
						$	237			$	—		$	(1,632	)	$	4,068
See Note E: “Debt” regarding derivatives related to convertible senior notes.

Debt

Debt	9 Months Ended
	Sep. 28, 2014
Debt	'
	E. Debt
	Loan Agreement
	On March 31, 2009, Teradyne K.K., Teradyne’s wholly-owned subsidiary in Japan, entered into a loan agreement with a local bank in Japan to borrow approximately $10.0 million (the loan was denominated in Japanese Yen). The loan had a term of 5 years and a fixed interest rate of 0.8%. Approximately $6.0 million of the loan was collateralized by a real estate mortgage on Teradyne K.K.’s building and land in Kumamoto, Japan and approximately $4.0 million was unsecured. Teradyne, Inc. guaranteed payment of the loan obligation. The loan was amortized over the term of the loan with semiannual principal payments of approximately $1.0 million on September 30 and March 30 each year. The final principal and interest payments were made in March 2014.
	Convertible Senior Notes
	In April 2009, Teradyne issued 4.50% convertible senior notes (the “Notes”) at an aggregate principal amount of $190 million and a conversion price of $5.4750 or 182.65 shares of Teradyne’s common stock per $1,000 principal amount of Notes. The Notes had a maturity date of March 15, 2014. Substantially all of the Notes were converted prior to March 15, 2014 and were “net share settled,” meaning that the holders received, for each $1,000 in principal amount of Notes, $1,000 in cash and approximately 131.95 shares of Teradyne common stock (calculated by taking 182.65 shares less 50.7 shares). The 50.7 shares were determined by dividing the $1,000 principal amount by the $19.74 average trading price of Teradyne’s common stock over the 25 day trading period from February 5, 2014 to March 12, 2014.
	Teradyne satisfied the Notes “net share settlement” by paying the aggregate principal amount of $190 million in cash and issuing 25.1 million shares of common stock. On March 13, 2014, Teradyne exercised its call option agreement entered into with Goldman, Sachs & Co. (the “hedge counterparty”) at the time of issuance of the Notes and received 25.1 million shares of Teradyne’s common stock, which were retired.
	From June 17, 2014 to September 17, 2014, the hedge counterparty exercised its warrant agreement entered into with Teradyne at the time of issuance of the Notes. The warrants were net share settled. In the three and nine months ended September 28, 2014, Teradyne issued 19.3 million and 21.2 million shares of its common stock, respectively, for warrants exercised at a weighted average strike price of $7.6348 and $7.6351, respectively.
	The tables below represent the components of Teradyne’s convertible senior notes:
		September 28,		December 31,
		2014		2013
		(in thousands)
	Debt principal	$	—	$	189,998
	Unamortized debt discount		—		4,290
	Net carrying amount of the convertible debt	$	—	$	185,708
	The interest expense on Teradyne’s convertible senior notes for the three and nine months ended September 28, 2014 and September 29, 2013 was as follows:
		For the Three Months				For the Nine Months
		Ended				Ended
		September 28,		September 29,		September 28,		September 29,
		2014		2013		2014		2013
		(in thousands)
	Contractual interest expense	$	—	$	2,114	$	1,757	$	6,388
	Amortization of the discount component and debt issue fees		—		4,221		4,493		12,266
	Total interest expense on the convertible debt	$	—	$	6,335	$	6,250	$	18,654

Prepayments

Prepayments	9 Months Ended
	Sep. 28, 2014
Prepayments	'
	F. Prepayments
	Prepayments consist of the following and are included in prepayments on the balance sheet:
		September 28,		December 31,
		2014		2013
		(in thousands)
	Contract manufacturer prepayments	$	68,126	$	115,388
	Prepaid maintenance and other services		6,794		6,538
	Prepaid taxes		3,413		3,281
	Other prepayments		10,399		11,167
	Total prepayments	$	88,732	$	136,374

Deferred_Revenue_and_Customer_

Deferred Revenue and Customer Advances	9 Months Ended
	Sep. 28, 2014
Deferred Revenue and Customer Advances	'
	G. 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:
		September 28,		December 31,
		2014		2013
		(in thousands)
	Extended warranty	$	43,497	$	34,909
	Equipment maintenance and training		27,703		22,455
	Customer advances		5,041		4,825
	Undelivered elements		7,185		6,971
	Total deferred revenue and customer advances	$	83,426	$	69,160

Product_Warranty

Product Warranty	9 Months Ended
	Sep. 28, 2014
Product Warranty	'
	H. Product Warranty
	Teradyne generally provides a one-year warranty on its products, commencing upon installation 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						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Balance at beginning of period	$	9,073		$	7,351		$	6,660		$	9,786
	Accruals for warranties issued during the period		4,419			3,674			12,675			8,781
	Adjustments related to pre-existing warranties		(559	)		(524	)		(1,000	)		(2,323	)
	Settlements made during the period		(2,982	)		(2,470	)		(8,384	)		(8,213	)
	Balance at end of period	$	9,951		$	8,031		$	9,951		$	8,031
	When Teradyne receives revenue for extended warranty beyond one year, it is deferred and recognized on a straight-line basis over the contract period. Related costs are expensed as incurred. The extended warranty balance below is included in short and long-term deferred revenue and customer advances on the balance sheet.
		For the Three Months						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Balance at beginning of period	$	40,052		$	34,854		$	34,909		$	26,987
	Deferral of new extended warranty revenue		9,896			5,586			24,218			17,791
	Recognition of extended warranty deferred revenue		(6,451	)		(4,120	)		(15,630	)		(8,458	)
	Balance at end of period	$	43,497		$	36,320		$	43,497		$	36,320

StockBased_Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 28, 2014
Stock-Based Compensation	'
	I. Stock-Based Compensation
	In January 2014, Teradyne granted 0.1 million of 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 will be measured against the Philadelphia Semiconductor Index, which consists of thirty companies in the semiconductor device and capital equipment industries. The final number of TSR PRSUs that vest will vary based upon the level of performance achieved from 200% of the target shares to 0% of the target shares. All TSR PRSUs will vest upon the three-year anniversary of the January 24, 2014 grant date. No TSR PRSUs will vest if the executive officer is no longer an employee at the end of the three-year period. 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 three-year service period. 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 the executive officer is not an employee at the end of the three-year service period. During the nine months ended September 28, 2014, Teradyne granted 0.1 million TSR performance-based restricted stock unit awards with an estimated grant date fair value of $22.06 per award. The fair value was estimated using the Monte Carlo simulation model with the following assumptions:
		For the Nine Months
		Ended
		September 28,
		2014
	Risk-free interest rate		0.75	%
	Teradyne volatility-historical		36.1	%
	Philadelphia Semiconductor Index volatility-historical		24.6	%
	Dividend yield		1.25	%
	Expected volatility was based on the historical volatility of Teradyne’s stock and the Philadelphia Semiconductor Index 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 $0.24 per share divided by Teradyne’s January 24, 2014 stock price of $19.16.
	During the nine months ended September 28, 2014, Teradyne granted 1.7 million of service-based restricted stock unit awards to employees at a weighted average grant date fair value of $19.09 and 0.1 million of service-based stock options to executive officers at a weighted average grant date fair value of $5.49.
	During the nine months ended September 29, 2013, Teradyne granted 1.9 million of service-based restricted stock unit awards to employees at a weighted average grant date fair value of $16.60 and 0.2 million of service-based stock options to executive officers at a weighted average grant date fair value of $6.09.
	Restricted stock unit awards granted to employees vest in equal annual installments over four years. Stock options vest in equal annual installments over four years, and have a term of seven years from the date of grant.
	The fair value of stock options was estimated using the Black-Scholes option-pricing model with the following assumptions:
		For the Nine Months
		Ended
		September 28,			September 29,
		2014			2013
	Expected life (years)		4			4
	Risk-free interest rate		1.2	%		0.6	%
	Volatility-historical		38.8	%		46.8	%
	Dividend yield		1.25	%		0	%
	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 $0.24 per share divided by Teradyne’s January 24, 2014 stock price of $19.16.
	Effective January 31, 2014, Michael Bradley retired as Chief Executive Officer of Teradyne. Mr. Bradley will continue to serve on Teradyne’s Board of Directors. On January 22, 2014, Teradyne entered into an agreement (the “Retirement Agreement”) with Mr. Bradley. Under the Retirement Agreement, Mr. Bradley’s unvested restricted stock units and stock options granted prior to his retirement date will continue to vest in accordance with their terms through January 31, 2017; and any vested options or options that vest during that period may be exercised for the remainder of the applicable option term. In the Retirement Agreement, Mr. Bradley agreed to be bound by non-competition and non-solicitation restrictions through January 31, 2017. In January 2014, Teradyne recorded a one-time charge to stock-based compensation expense of $6.6 million related to the Retirement Agreement.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 28, 2014
Accumulated Other Comprehensive Income	'
	J. Accumulated Other Comprehensive Income
	Changes in accumulated other comprehensive income, which is presented net of tax, consist of the following:
			Unrealized			Retirement			Total
			Gains on			Plans Prior
			Marketable			Service
			Securities			Credit
			(in thousands)
	Balance at December 31, 2013, net of tax of $794, $(284)		$	1,381		$	2,619		$	4,000
	Other comprehensive income before reclassifications, net of tax of $1,103, $0			2,166			—			2,166
	Amounts reclassified from accumulated other comprehensive income, net of tax of $(591), $(127)			(1,086	)		(221	)		(1,307	)
	Net current period other comprehensive income			1,080			(221	)		859
	Balance at September 28, 2014, net of tax of $1,306, $(411)		$	2,461		$	2,398		$	4,859
	Reclassifications out of accumulated other comprehensive income to the statement of operations for the three and nine months ended September 28, 2014 and September 29, 2013 were as follows:
	Details about Accumulated Other Comprehensive Income		For the Three Months						For the Nine Months					Affected Line Item
	Components		Ended						Ended					in the Statements
														of Operations
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Available-for-sale marketable securities:
	Unrealized gains, net of tax of $348, $109, $591, $231		$	638		$	189		$	1,086		$	401		Interest income
	Amortization of defined benefit pension and postretirement plans:
	Prior service benefit, net of tax of $42, $40, $127, $119			74			69			221			207		(a)
	Total reclassifications		$	712		$	258		$	1,307		$	608		Net income
	(a)	The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit; see Note N: “Retirement Plans.”

Intangible_Assets

Intangible Assets	9 Months Ended
	Sep. 28, 2014
Intangible Assets	'
	K. Intangible Assets
	Amortizable intangible assets consist of the following and are included in intangible assets, net on the balance sheet:
		September 28, 2014
		Gross		Accumulated		Net		Weighted
		Carrying		Amortization		Carrying		Average
		Amount				Amount		Useful Life
		(in thousands)
	Developed technology	$	342,933	$	212,949	$	129,984		6.2 years
	Customer relationships		141,005		90,244		50,761		8.0 years
	Trade names and trademarks		30,034		13,302		16,732		9.1 years
	Total intangible assets	$	513,972	$	316,495	$	197,477		6.9 years
		December 31, 2013
		Gross		Accumulated		Net		Weighted
		Carrying		Amortization		Carrying		Average
		Amount				Amount		Useful Life
		(in thousands)
	Developed technology	$	342,933	$	174,563	$	168,370		6.2 years
	Customer relationships		141,497		76,963		64,534		8.0 years
	Trade names and trademarks		30,034		10,647		19,387		9.1 years
	Customer backlog		1,000		1,000		—		0.4 years
	Total intangible assets	$	515,464	$	263,173	$	252,291		6.9 years
	Aggregate intangible asset amortization expense was $18.3 million and $54.8 million, respectively, for the three and nine months ended September 28, 2014 and $18.1 million and $54.2 million, respectively, for the three and nine months ended September 29, 2013. Estimated intangible asset amortization expense for each of the five succeeding fiscal years is as follows:
	Year	Amortization Expense
		(in thousands)
	2014 (remainder)	$	15,327
	2015		53,391
	2016		53,391
	2017		47,232
	2018		22,691
	Thereafter		5,445

Net_Income_per_Common_Share

Net Income per Common Share	9 Months Ended
	Sep. 28, 2014
Net Income per Common Share	'
	L. 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				For the Nine Months
			Ended				Ended
			September 28,		September 29,		September 28,		September 29,
			2014		2013		2014		2013
			(in thousands, except per share amounts)
	Net income for basic and diluted net income per share		$	82,949	$	69,459	$	185,083	$	142,604
	Weighted average common shares-basic			207,381		191,307		198,367		190,521
	Effect of dilutive potential common shares:
	Incremental shares from assumed conversion of convertible notes (1)			—		23,257		6,684		23,303
	Convertible note hedge warrant shares (2)			8,885		18,678		16,744		18,742
	Restricted stock units			1,167		1,102		975		1,000
	Stock options			879		1,465		997		1,564
	Employee stock purchase rights			21		19		28		35
	Dilutive potential common shares			10,952		44,521		25,428		44,644
	Weighted average common shares-diluted			218,333		235,828		223,795		235,165
	Net income per common share-basic		$	0.4	$	0.36	$	0.93	$	0.75
	Net income per common share-diluted		$	0.38	$	0.29	$	0.83	$	0.61
	-1	Incremental shares from conversion of the convertible notes for the nine months ended September 28, 2014 were calculated using the difference between the average Teradyne stock price from January 1, 2014 through March 12, 2014 and the conversion price of $5.4750, multiplied by 34.7 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 from January 1, 2014 to March 12, 2014 and adjusted for the number of days the convertible notes were outstanding. Incremental shares from assumed conversion of the convertible notes for the three and nine months ended September 29, 2013 were calculated using the difference between the average Teradyne stock price for the period the convertible notes were outstanding and the conversion price of $5.48, multiplied by the 34.7 million shares to be issued upon conversion. 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 note hedge warrant shares for the three and nine months ended September 28, 2014 are calculated using the difference between the average Teradyne stock price for the period the warrants were outstanding and the warrant price of $7.63 and $7.64, respectively, multiplied by the weighted average warrant shares outstanding. The result of this calculation, representing the total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period the warrants were outstanding. Convertible note hedge warrant shares for the three and nine months ended September 29, 2013 are calculated using the difference between the average Teradyne stock price for the period and the warrant price of $7.67, multiplied by the 34.7 million shares that would be issued upon conversion. The result of this calculation, representing the total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period.
	The computation of diluted net income per common share for the three and nine months ended September 28, 2014 excludes the effect of the potential exercise of stock options to purchase approximately 0.3 million shares because the effect would have been anti-dilutive.
	The computation of diluted net income per common share for the three and nine months ended September 29, 2013 excludes the effect of the potential exercise of stock options to purchase approximately 0.4 million shares because the effect would have been anti-dilutive.

Restructuring_and_Other

Restructuring and Other	9 Months Ended
	Sep. 28, 2014
Restructuring and Other	'
	M. Restructuring and Other
	Restructuring
	During the nine months ended September 28, 2014, Teradyne recorded $0.8 million of severance charges related to headcount reductions of approximately 30 people, primarily in Wireless Test. During the nine months ended September 29, 2013, Teradyne recorded $1.5 million of severance charges related to headcount reductions of approximately 40 people, of which $1.4 million was in System Test and $0.4 million was in Semiconductor Test, and a $(0.4) million credit in Corporate for a change in the estimated exit costs related to a leased facility.
		Severance			Facility			Total
		and			Exit
		Benefits			Costs
		(in thousands)
	Pre-2013 Activities
	Balance at December 31, 2012	$	243		$	1,084		$	1,327
	Change in estimate		—			(553	)		(553	)
	Cash payments		(243	)		(531	)		(774	)
	Balance at December 31, 2013	$	—		$	—		$	—
	2013 Activities
	Q3 2013 Activity:
	Provision	$	1,337		$	—		$	1,337
	Cash payments		(966	)		—			(966	)
	Balance at December 31, 2013		371			—			371
	Cash payments		(161	)		—			(161	)
	Balance at March 30, 2014		210			—			210
	Cash payments		—			—			—
	Balance at June 29, 2014		210			—			210
	Cash payments		—			—			—
	Balance at September 28, 2014	$	210		$	—		$	210
	Q4 2013 Activity:
	Provision	$	600		$	—		$	600
	Cash payments		(486	)		—			(486	)
	Balance at December 31, 2013		114			—			114
	Cash payments		(114	)		—			(114	)
	Balance at March 30, 2014	$	—		$	—		$	—
		Severance			Facility			Total
		and			Exit
		Benefits			Costs
		(in thousands)
	2014 Activities
	Q2 2014 Activity:
	Provision	$	572		$	—		$	572
	Cash payments		(530	)		—			(530	)
	Balance at June 29, 2014		42			—			42
	Cash payments		(42	)		—			(42	)
	Balance at September 28, 2014	$	—		$	—		$	—
	Q3 2014 Activity:
	Provision	$	225		$	—		$	225
	Cash payments		(225	)		—			(225	)
	Balance at September 28, 2014	$	—		$	—		$	—
	Balance at September 28, 2014	$	210		$	—		$	210
	The accrual balance for severance and benefits of $0.2 million is reflected in the accrued employees’ compensation and withholdings on the balance sheet and is expected to be paid by December 2014.
	Other
	During the three and nine months ended September 28, 2014, Teradyne recorded a $0.6 million fair value adjustment to decrease the ZTEC acquisition contingent consideration.

Retirement_Plans

Retirement Plans	9 Months Ended
	Sep. 28, 2014
Retirement Plans	'
	N. Retirement Plans
	ASC 715, “Compensation—Retirement Benefits” requires an employer with defined benefit plans or other postretirement benefit plans to recognize an asset or a liability on its balance sheet for the overfunded or underfunded status of the plans as defined by ASC 715. The pension asset or liability represents a difference between the fair value of the pension plan’s assets and the projected benefit obligation.
	On October 27, 2014, the U.S. Society of Actuaries released new mortality tables. Teradyne will use the new mortality tables along with other updated pension valuation assumptions (discount rate, asset rate of return, etc.) as part of its annual fourth quarter pension obligation remeasurement. The estimated actuarial loss as a result of the new mortality tables and current discount rates is approximately $50 million.
	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 these plans consist primarily of fixed income and equity securities. In addition, Teradyne has 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”), as well as unfunded foreign plans. In the nine months ended September 28, 2014, Teradyne contributed $1.3 million to the U.S. supplemental executive defined benefit pension plan and $1.2 million to certain qualified plans for non-U.S. subsidiaries.
	For the three and nine months ended September 28, 2014 and September 29, 2013, Teradyne’s net periodic pension cost was comprised of the following:
		For the Three Months						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Service cost	$	761		$	871		$	2,368		$	2,557
	Interest cost		3,650			3,350			11,102			10,001
	Expected return on plan assets		(3,335	)		(3,664	)		(10,060	)		(10,925	)
	Amortization of unrecognized prior service cost		34			41			101			123
	Actuarial loss (gain)		—			—			362			(1,123	)
	Total net periodic pension cost	$	1,110		$	598		$	3,873		$	633
	Postretirement Benefit Plan
	In addition to receiving pension benefits, U.S. Teradyne employees who meet early retirement eligibility requirements as of their termination dates may participate in Teradyne’s Welfare Plan, which includes death, and 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 and nine months ended September 28, 2014 and September 29, 2013, Teradyne’s net periodic postretirement benefit was comprised of the following:
		For the Three Months						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Service cost	$	15		$	19		$	44		$	56
	Interest cost		84			86			252			257
	Amortization of unrecognized prior service benefit		(150	)		(150	)		(449	)		(449	)
	Actuarial gain		—			—			(247	)		(236	)
	Total net periodic post-retirement benefit	$	(51	)	$	(45	)	$	(400	)	$	(372	)

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 28, 2014
Commitments and Contingencies	'
	O. Commitments and Contingencies
	Purchase Commitments
	As of September 28, 2014, Teradyne had entered into purchase commitments for certain components and materials. The purchase commitments covered by the agreements aggregate to approximately $155.2 million, of which $147.4 million is for less than one year.
	Legal Claims
	Teradyne is subject to various legal proceedings and claims which have arisen 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 Teradyne’s results of operations, financial condition or cash flows.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 28, 2014
Income Taxes	'
	P. Income Taxes
	The effective tax rate for the three months ended September 28, 2014 and September 29, 2013 was 18% and 21%, respectively. The decrease in the tax rate was primarily due to a more favorable geographic mix of income partially offset by an increase in reserves for uncertain tax positions.
	The effective tax rate for the nine months ended September 28, 2014 and September 29, 2013 was 16% and 14%, respectively. The increase in the tax rate was primarily due to income tax expense for the nine months ended September 29, 2013 being reduced for a discrete tax benefit from the January 2013 reinstatement of the U.S. research and development credit for fiscal year 2012 and an increase in reserves for uncertain tax positions in fiscal year 2014, partially offset by a more favorable geographic mix of income in fiscal year 2014.
	The effective tax rate for each of these periods is lower than the 35% U.S. statutory federal tax rate primarily due to the geographic mix of income and profits earned by Teradyne’s international subsidiaries being taxed at rates lower than the U.S. statutory rate.
	As of September 28, 2014, Teradyne had $31.6 million of reserves for uncertain tax positions. As of December 31, 2013, Teradyne had $21.2 million of reserves for uncertain tax positions. The $10.4 million net increase in reserves for uncertain tax positions primarily relates to the allocation of income among jurisdictions. As of September 28, 2014, Teradyne anticipates the liability for uncertain tax positions could decrease by approximately $2.8 million over the next twelve months, primarily as a result of the expiration of statutes of limitations and clarification of tax laws. The potential decrease is primarily related to equity compensation.
	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 nine months ended September 28, 2014 were $12.3 million or $0.05 per diluted share. The tax holiday is currently expected to expire on December 31, 2015.

Segment_Information

Segment Information	9 Months Ended
	Sep. 28, 2014
Segment Information	'
	Q. Segment Information
	Teradyne has three operating segments (Semiconductor Test, Wireless Test and System Test), which are its reportable segments. The Semiconductor Test segment includes operations related to the design, manufacturing and marketing of semiconductor test products and services. The Wireless Test segment includes operations related to design, manufacturing and marketing of wireless test products and services. The System Test segment includes operations related to design, manufacturing and marketing of products and services for military/aerospace instrumentation test, storage test and circuit-board test. Each operating segment has a segment manager who is directly accountable to and maintains regular contact with Teradyne’s chief operating decision maker (Teradyne’s chief executive officer) to discuss operating activities, financial results, forecasts, and plans for the segment.
	Teradyne evaluates performance based on several factors, of which the primary financial measure is business segment income before income taxes. The accounting policies of the business segments are the same as those described in Note B: “Accounting Policies” in Teradyne’s Annual Report on Form 10-K for the year ended December 31, 2013. Segment information is as follows:
			Semiconductor			Wireless			System			Corporate			Consolidated
			Test			Test			Test			and
												Eliminations
			(in thousands)
	Three months ended September 28, 2014:
	Net revenues		$	380,083		$	54,838		$	43,089		$	—		$	478,010
	Income before income taxes(1)(2)			91,900			2,379			5,779			612			100,670
	Three months ended September 29, 2013:
	Net revenues		$	304,131		$	93,132		$	36,113		$	—		$	433,376
	Income (loss) before income taxes(1)(2)			68,932			27,575			(2,462	)		(6,493	)		87,552
	Nine months ended September 28, 2014:
	Net revenues		$	1,063,254		$	144,747		$	116,586		$	—		$	1,324,587
	Income (loss) before income taxes(1)(2)			233,770			(8,477	)		5,512			(10,616	)		220,189
	Nine months ended September 29, 2013:
	Net revenues		$	808,068		$	226,116		$	108,448		$	—		$	1,142,632
	Income (loss) before income taxes(1)(2)			141,304			41,491			(153	)		(16,159	)		166,483
	-1	Pension and postretirement actuarial gains and losses, interest income, and interest expense and other are included in Corporate and Eliminations.
	-2	Included in the income (loss) before income taxes for each of the segments are charges and credits for the three and nine months ended September 28, 2014 and September 29, 2013 that include restructuring and other, and provision for excess and obsolete inventory, as follows:
	Included in the Semiconductor Test segment are charges for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Cost of revenues—provision for excess and obsolete inventory		$	4,404		$	1,378		$	14,322		$	1,878
	Restructuring and other			—			282			—			416
	Total		$	4,404		$	1,660		$	14,322		$	2,294
	Included in the Wireless Test segment are charges for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Cost of revenues—provision for excess and obsolete inventory		$	1,267		$	2,059		$	5,239		$	6,125
	Restructuring and other			—			—			426			82
	Total		$	1,267		$	2,059		$	5,665		$	6,207
	Included in the System Test segment are charges for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Cost of revenues—provision for excess and obsolete inventory		$	763		$	404		$	1,944		$	1,613
	Restructuring and other			225			1,055			371			1,430
	Total		$	988		$	1,459		$	2,315		$	3,043
	Included in Corporate and Eliminations are credits for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Restructuring and other		$	(630	)	$	(448	)	$	(630	)	$	(448	)
	Total		$	(630	)	$	(448	)	$	(630	)	$	(448	)

Shareholders_Equity

Shareholders' Equity	9 Months Ended
	Sep. 28, 2014
Shareholders' Equity	'
	R. Shareholders’ Equity
	Stock Repurchase Program
	In November 2010, Teradyne’s Board of Directors authorized a stock repurchase program for up to $200 million. In the three and nine months ended September 28, 2014 and September 29, 2013, Teradyne did not repurchase any shares. The cumulative repurchases under the new program as of September 28, 2014 totaled 2.6 million shares of common stock for $31.2 million at an average price of $11.84.
	Dividend
	Holders of Teradyne’s common stock are entitled to receive dividends when they are declared by Teradyne’s Board of Directors. In January 2014, Teradyne’s Board of Directors declared an initial quarterly cash dividend of $0.06 per share that was paid on June 2, 2014 to stockholders of record as of May 9, 2014. In August 2014, Teradyne’s Board of Directors declared a quarterly cash dividend of $0.06 per share that was paid on September 26, 2014 to stockholders of record as of September 5, 2014. Dividend payments for the three and nine months ended September 28, 2014 were $12.8 million and $24.4 million, respectively. Payment of future cash dividends will rest within the discretion of Teradyne’s Board of Directors and will depend, among other things, upon Teradyne’s earnings, capital requirements and financial condition.

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 28, 2014
Subsequent Events	'
	S. Subsequent Events
	On October 31, 2014, Teradyne completed the acquisition of substantially all the assets of Avionics Interface Technologies, LLC (“AIT”) located in Omaha, Nebraska, for approximately $18.9 million and up to $2.1 million payable upon achievement of certain revenue and gross margin targets through December 31, 2016. The fair value of assets and liabilities acquired has not been disclosed because Teradyne has not completed the valuation. AIT is a leading provider of equipment for testing state-of-the-art data buses. The acquisition complements Teradyne’s Mil/Aero line of bus test instrumentation for commercial and defense avionics systems. AIT will be included in Teradyne’s System Test segment.

Accounting_Policies_Policies

Accounting Policies (Policies)	9 Months Ended
	Sep. 28, 2014
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 presentation of such interim financial statements. Certain prior year’s amounts were reclassified to conform to the current year presentation. The December 31, 2013 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 February 28, 2014, for the year ended December 31, 2013.
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.

Financial_Instruments_and_Deri1

Financial Instruments and Derivatives (Tables)	9 Months Ended
	Sep. 28, 2014
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 September 28, 2014 and December 31, 2013.
			September 28, 2014
			Quoted Prices				Significant				Significant			Total
			in Active				Other				Unobservable
			Markets for				Observable				Inputs
			Identical				Inputs				(Level 3)
			Instruments				(Level 2)
			(Level 1)
			(in thousands)
	Assets
	Cash		$	100,633			$	—			$	—		$	100,633
	Cash equivalents			99,979				11,092				—			111,071
	Available-for-sale securities:
	U.S. Treasury securities			—				459,240				—			459,240
	U.S. government agency securities			—				285,617				—			285,617
	Commercial paper			—				99,774				—			99,774
	Corporate debt securities			—				94,357				—			94,357
	Certificates of deposit and time deposits			—				18,522				—			18,522
	Equity and debt mutual funds			12,099				—				—			12,099
	Total		$	212,711			$	968,602			$	—		$	1,181,313
	Liabilities
	Contingent consideration		$	—			$	—			$	1,600		$	1,600
	Derivatives			—				546				—			546
	Total		$	—			$	546			$	1,600		$	2,146
	Reported as follows:
			(Level 1)				(Level 2)				(Level 3)			Total
			(in thousands)
	Assets
	Cash and cash equivalents		$	200,612			$	11,092			$	—		$	211,704
	Marketable securities			—				594,801				—			594,801
	Long-term marketable securities			12,099				362,709				—			374,808
			$	212,711			$	968,602			$	—		$	1,181,313
	Liabilities
	Other accrued liabilities		$	—			$	546			$	—		$	546
	Long-term other accrued liabilities			—				—				1,600			1,600
			$	—			$	546			$	1,600		$	2,146
			December 31, 2013
			Quoted Prices				Significant				Significant			Total
			in Active				Other				Unobservable
			Markets for				Observable				Inputs
			Identical				Inputs				(Level 3)
			Instruments				(Level 2)
			(Level 1)
			(in thousands)
	Assets
	Cash		$	117,242			$	—			$	—		$	117,242
	Cash equivalents			165,865				58,531				—			224,396
	Available-for-sale securities:
	U.S. Treasury securities			—				467,895				—			467,895
	U.S. government agency securities			—				202,588				—			202,588
	Commercial paper			—				105,598				—			105,598
	Corporate debt securities			—				65,387				—			65,387
	Equity and debt mutual funds			13,156				—				—			13,156
	Certificates of deposit and time deposits			—				3,258				—			3,258
	Non-U.S. government securities			—				78				—			78
	Total			296,263				903,335				—			1,199,598
	Derivatives			—				153				—			153
	Total		$	296,263			$	903,488			$	—		$	1,199,751
	Liabilities
	Contingent consideration		$	—			$	—			$	2,230		$	2,230
	Total		$	—			$	—			$	2,230		$	2,230
	Reported as follows:
			(Level 1)				(Level 2)				(Level 3)			Total
		(in thousands)
Assets
Cash and cash equivalents		$	283,107			$	58,531			$	—		$	341,638
Marketable securities			—				586,882				—			586,882
Long-term marketable securities			13,156				257,922				—			271,078
Other current assets			—				153				—			153
		$	296,263			$	903,488			$	—		$	1,199,751
Liabilities
Long-term other accrued liabilities		$	—			$	—			$	2,230		$	2,230
		$	—			$	—			$	2,230		$	2,230
Schedule of Changes in Fair Value of Level 3 Contingent Consideration	'
	Changes in the fair value of Level 3 contingent consideration for the three and nine months ended September 28, 2014 and September 29, 2013 were as follows:
	Contingent consideration related to Teradyne’s acquisition of ZTEC		For the Three and Nine Months
	in October 2013		Ended
			28-Sep-14
			(in thousands)
	Balance at December 31, 2013		$	2,230
	Contingent consideration payments			—
	Balance at March 30, 2014			2,230
	Contingent consideration payments			—
	Balance at June 29, 2014			2,230
	Fair value adjustment			(630	)
	Balance at September 28, 2014		$	1,600
	Contingent consideration related to Teradyne’s acquisition of LitePoint		For the Three and Nine Months
	in October 2011		Ended
			29-Sep-13
			(in thousands)
	Balance at December 31, 2012		$	388
	Contingent consideration payments			(313	)
	Balance at March 31, 2013			75
	Contingent consideration payments			(75	)
	Balance at June 30, 2013			—
	Contingent consideration payments			—
	Balance at September 29, 2013		$	—
Schedule of Carrying Amounts and Fair Values of Financial Instruments	'
	The carrying amounts and fair values of Teradyne’s financial instruments at September 28, 2014 and December 31, 2013 were as follows:
			September 28, 2014								December 31, 2013
			Carrying Value				Fair Value				Carrying Value			Fair Value
			(in thousands)
	Cash and cash equivalents		$	211,704			$	211,704			$	341,638		$	341,638
	Marketable securities			969,609				969,609				857,960			857,960
	Convertible debt(1)			—				—				185,708			611,433
	Japan loan			—				—				955			955
	-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 feature.
Schedule of Available-for-Sale Marketable Securities	'
	The following tables summarize the composition of available-for-sale marketable securities at September 28, 2014 and December 31, 2013:
			September 28, 2014
			Available-for-Sale														Fair Market
																	Value of
																	Investments
																	with Unrealized
			Cost				Unrealized				Unrealized			Fair Market			Losses
							Gain				(Loss)			Value
			(in thousands)
	U.S. Treasury securities		$	458,958			$	373			$	(91	)	$	459,240		$	64,267
	U.S. government agency securities			285,528				195				(106	)		285,617			66,700
	Commercial paper			99,767				11				(4	)		99,774			23,722
	Corporate debt securities			92,883				1,734				(260	)		94,357			56,393
	Certificates of deposit and time deposits			18,508				14				—			18,522			—
	Equity and debt mutual funds			10,199				1,933				(33	)		12,099			1,074
			$	965,843			$	4,260			$	(494	)	$	969,609		$	212,156
	Reported as follows:
			Cost				Unrealized				Unrealized			Fair Market			Fair Market
							Gain				(Loss)			Value			Value of
																	Investments
																	with Unrealized
																	Losses
			(in thousands)
	Marketable securities		$	594,500			$	319			$	(18	)	$	594,801		$	66,188
	Long-term marketable securities			371,343				3,941				(476	)		374,808			145,968
			$	965,843			$	4,260			$	(494	)	$	969,609		$	212,156
			December 31, 2013
			Available-for-Sale														Fair Market
																	Value of
																	Investments
																	with Unrealized
			Cost				Unrealized				Unrealized			Fair Market			Losses
							Gain				(Loss)			Value
			(in thousands)
	U.S. Treasury securities		$	468,084			$	94			$	(283	)	$	467,895		$	108,212
	U.S. government agency securities			202,573				75				(60	)		202,588			84,498
	Commercial paper			105,583				16				(1	)		105,598			7,993
	Corporate debt securities			65,747				762				(1,122	)		65,387			40,355
	Equity and debt mutual funds			10,463				2,742				(49	)		13,156			702
	Certificates of deposit and time deposits			3,258				—				—			3,258			—
	Non-U.S. government securities			78				—				—			78			—
			$	855,786			$	3,689			$	(1,515	)	$	857,960		$	241,760
	Reported as follows:
			Cost				Unrealized				Unrealized			Fair Market			Fair Market
							Gain				(Loss)			Value			Value of
																	Investments
																	with Unrealized
																	Losses
			(in thousands)
	Marketable securities		$	586,818			$	85			$	(21	)	$	586,882		$	137,670
	Long-term marketable securities			268,968				3,604				(1,494	)		271,078			104,090
			$	855,786			$	3,689			$	(1,515	)	$	857,960		$	241,760
Contractual Maturities of Investments Held	'
	The contractual maturities of investments held at September 28, 2014 were as follows:
			September 28, 2014
			Cost				Fair Market
							Value
			(in thousands)
	Due within one year		$	594,500			$	594,801
	Due after 1 year through 5 years			330,340				330,412
	Due after 5 years through 10 years			5,772				5,859
	Due after 10 years			25,032				26,438
	Total		$	955,644			$	957,510
Schedule of Derivative Instruments in Statement of Financial Position at Fair Value	'
	The following table summarizes the fair value of derivative instruments at September 28, 2014 and December 31, 2013:
			Balance Sheet Location		September 28,				December 31,
					2014				2013
					(in thousands)
	Derivatives not designated as hedging instruments:
	Foreign currency forward contracts		Other current assets		$	—			$	153
			Other accrued liabilities			546				—
					$	546			$	153
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 during the three and nine months ended September 28, 2014 and September 29, 2013. The table does not reflect the corresponding gains (losses) from the remeasurement of the monetary assets and liabilities denominated in foreign currencies. For the three and nine months ended September 28, 2014, (losses) gains from the remeasurement of the monetary assets and liabilities denominated in foreign currencies were $(0.4) million and $0.9 million, respectively. For the three and nine months ended September 29, 2013, losses from the remeasurement of the monetary assets and liabilities denominated in foreign currencies were $(0.4) million and $(5.0) million, respectively.
			Location of Gains				For the Three Months							For the Nine Months
			(Losses)				Ended							Ended
			Recognized in
			Statement
			of Operations				September 28,				September 29,			September 28,			September 29,
							2014				2013			2014			2013
							(in thousands)
	Derivatives not designated as hedging instruments:
	Foreign exchange contracts			Interest expense and other			$	237			$	—		$	(1,632	)	$	4,068
							$	237			$	—		$	(1,632	)	$	4,068

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 28, 2014
Components of Convertible Senior Notes	'
	The tables below represent the components of Teradyne’s convertible senior notes:
		September 28,		December 31,
		2014		2013
		(in thousands)
	Debt principal	$	—	$	189,998
	Unamortized debt discount		—		4,290
	Net carrying amount of the convertible debt	$	—	$	185,708
Interest Expense on Convertible Senior Notes	'
	The interest expense on Teradyne’s convertible senior notes for the three and nine months ended September 28, 2014 and September 29, 2013 was as follows:
		For the Three Months				For the Nine Months
		Ended				Ended
		September 28,		September 29,		September 28,		September 29,
		2014		2013		2014		2013
		(in thousands)
	Contractual interest expense	$	—	$	2,114	$	1,757	$	6,388
	Amortization of the discount component and debt issue fees		—		4,221		4,493		12,266
	Total interest expense on the convertible debt	$	—	$	6,335	$	6,250	$	18,654

Prepayments_Tables

Prepayments (Tables)	9 Months Ended
	Sep. 28, 2014
Schedule of Prepayments	'
	Prepayments consist of the following and are included in prepayments on the balance sheet:
		September 28,		December 31,
		2014		2013
		(in thousands)
	Contract manufacturer prepayments	$	68,126	$	115,388
	Prepaid maintenance and other services		6,794		6,538
	Prepaid taxes		3,413		3,281
	Other prepayments		10,399		11,167
	Total prepayments	$	88,732	$	136,374

Deferred_Revenue_and_Customer_1

Deferred Revenue and Customer Advances (Tables)	9 Months Ended
	Sep. 28, 2014
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:
		September 28,		December 31,
		2014		2013
		(in thousands)
	Extended warranty	$	43,497	$	34,909
	Equipment maintenance and training		27,703		22,455
	Customer advances		5,041		4,825
	Undelivered elements		7,185		6,971
	Total deferred revenue and customer advances	$	83,426	$	69,160

Product_Warranty_Tables

Product Warranty (Tables)	9 Months Ended
	Sep. 28, 2014
Other Accrued Liabilities	'
	The warranty balance below is included in other accrued liabilities on the balance sheet.
		For the Three Months						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Balance at beginning of period	$	9,073		$	7,351		$	6,660		$	9,786
	Accruals for warranties issued during the period		4,419			3,674			12,675			8,781
	Adjustments related to pre-existing warranties		(559	)		(524	)		(1,000	)		(2,323	)
	Settlements made during the period		(2,982	)		(2,470	)		(8,384	)		(8,213	)
	Balance at end of period	$	9,951		$	8,031		$	9,951		$	8,031
Extended Product Warranty of Short and Long-Term Deferred Revenue and Customer Advances	'
	The extended warranty balance below is included in short and long-term deferred revenue and customer advances on the balance sheet.
		For the Three Months						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Balance at beginning of period	$	40,052		$	34,854		$	34,909		$	26,987
	Deferral of new extended warranty revenue		9,896			5,586			24,218			17,791
	Recognition of extended warranty deferred revenue		(6,451	)		(4,120	)		(15,630	)		(8,458	)
	Balance at end of period	$	43,497		$	36,320		$	43,497		$	36,320

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 28, 2014
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 Nine Months
		Ended
		September 28,
		2014
	Risk-free interest rate		0.75	%
	Teradyne volatility-historical		36.1	%
	Philadelphia Semiconductor Index volatility-historical		24.6	%
	Dividend yield		1.25	%
Schedule of Estimated Fair Value of Stock Options Assumptions	'
	The fair value of stock options was estimated using the Black-Scholes option-pricing model with the following assumptions:
		For the Nine Months
		Ended
		September 28,			September 29,
		2014			2013
	Expected life (years)		4			4
	Risk-free interest rate		1.2	%		0.6	%
	Volatility-historical		38.8	%		46.8	%
	Dividend yield		1.25	%		0	%

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 28, 2014
Changes in Accumulated Other Comprehensive Income	'
	Changes in accumulated other comprehensive income, which is presented net of tax, consist of the following:
			Unrealized			Retirement			Total
			Gains on			Plans Prior
			Marketable			Service
			Securities			Credit
			(in thousands)
	Balance at December 31, 2013, net of tax of $794, $(284)		$	1,381		$	2,619		$	4,000
	Other comprehensive income before reclassifications, net of tax of $1,103, $0			2,166			—			2,166
	Amounts reclassified from accumulated other comprehensive income, net of tax of $(591), $(127)			(1,086	)		(221	)		(1,307	)
	Net current period other comprehensive income			1,080			(221	)		859
	Balance at September 28, 2014, net of tax of $1,306, $(411)		$	2,461		$	2,398		$	4,859
Reclassification Out of Accumulated Other Comprehensive Income to Statement of Operations	'
	Reclassifications out of accumulated other comprehensive income to the statement of operations for the three and nine months ended September 28, 2014 and September 29, 2013 were as follows:
	Details about Accumulated Other Comprehensive Income		For the Three Months						For the Nine Months					Affected Line Item
	Components		Ended						Ended					in the Statements
														of Operations
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Available-for-sale marketable securities:
	Unrealized gains, net of tax of $348, $109, $591, $231		$	638		$	189		$	1,086		$	401		Interest income
	Amortization of defined benefit pension and postretirement plans:
	Prior service benefit, net of tax of $42, $40, $127, $119			74			69			221			207		(a)
	Total reclassifications		$	712		$	258		$	1,307		$	608		Net income
	(a)	The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit; see Note N: “Retirement Plans.”

Intangible_Assets_Tables

Intangible Assets (Tables)	9 Months Ended
	Sep. 28, 2014
Schedule of Amortizable Intangible Assets	'
	Amortizable intangible assets consist of the following and are included in intangible assets, net on the balance sheet:
		September 28, 2014
		Gross		Accumulated		Net		Weighted
		Carrying		Amortization		Carrying		Average
		Amount				Amount		Useful Life
		(in thousands)
	Developed technology	$	342,933	$	212,949	$	129,984		6.2 years
	Customer relationships		141,005		90,244		50,761		8.0 years
	Trade names and trademarks		30,034		13,302		16,732		9.1 years
	Total intangible assets	$	513,972	$	316,495	$	197,477		6.9 years
		December 31, 2013
		Gross		Accumulated		Net		Weighted
		Carrying		Amortization		Carrying		Average
		Amount				Amount		Useful Life
		(in thousands)
	Developed technology	$	342,933	$	174,563	$	168,370		6.2 years
	Customer relationships		141,497		76,963		64,534		8.0 years
	Trade names and trademarks		30,034		10,647		19,387		9.1 years
	Customer backlog		1,000		1,000		—		0.4 years
	Total intangible assets	$	515,464	$	263,173	$	252,291		6.9 years
Schedule of Estimated Intangible Asset Amortization Expense	'
	Estimated intangible asset amortization expense for each of the five succeeding fiscal years is as follows:
	Year	Amortization Expense
		(in thousands)
	2014 (remainder)	$	15,327
	2015		53,391
	2016		53,391
	2017		47,232
	2018		22,691
	Thereafter		5,445

Net_Income_per_Common_Share_Ta

Net Income per Common Share (Tables)	9 Months Ended
	Sep. 28, 2014
Computation of Basic and Diluted 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				For the Nine Months
			Ended				Ended
			September 28,		September 29,		September 28,		September 29,
			2014		2013		2014		2013
			(in thousands, except per share amounts)
	Net income for basic and diluted net income per share		$	82,949	$	69,459	$	185,083	$	142,604
	Weighted average common shares-basic			207,381		191,307		198,367		190,521
	Effect of dilutive potential common shares:
	Incremental shares from assumed conversion of convertible notes (1)			—		23,257		6,684		23,303
	Convertible note hedge warrant shares (2)			8,885		18,678		16,744		18,742
	Restricted stock units			1,167		1,102		975		1,000
	Stock options			879		1,465		997		1,564
	Employee stock purchase rights			21		19		28		35
	Dilutive potential common shares			10,952		44,521		25,428		44,644
	Weighted average common shares-diluted			218,333		235,828		223,795		235,165
	Net income per common share-basic		$	0.4	$	0.36	$	0.93	$	0.75
	Net income per common share-diluted		$	0.38	$	0.29	$	0.83	$	0.61
	-1	Incremental shares from conversion of the convertible notes for the nine months ended September 28, 2014 were calculated using the difference between the average Teradyne stock price from January 1, 2014 through March 12, 2014 and the conversion price of $5.4750, multiplied by 34.7 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 from January 1, 2014 to March 12, 2014 and adjusted for the number of days the convertible notes were outstanding. Incremental shares from assumed conversion of the convertible notes for the three and nine months ended September 29, 2013 were calculated using the difference between the average Teradyne stock price for the period the convertible notes were outstanding and the conversion price of $5.48, multiplied by the 34.7 million shares to be issued upon conversion. 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 note hedge warrant shares for the three and nine months ended September 28, 2014 are calculated using the difference between the average Teradyne stock price for the period the warrants were outstanding and the warrant price of $7.63 and $7.64, respectively, multiplied by the weighted average warrant shares outstanding. The result of this calculation, representing the total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period the warrants were outstanding. Convertible note hedge warrant shares for the three and nine months ended September 29, 2013 are calculated using the difference between the average Teradyne stock price for the period and the warrant price of $7.67, multiplied by the 34.7 million shares that would be issued upon conversion. The result of this calculation, representing the total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period.

Restructuring_and_Other_Tables

Restructuring and Other (Tables)	9 Months Ended
	Sep. 28, 2014
Restructuring and Other	'
		Severance			Facility			Total
		and			Exit
		Benefits			Costs
		(in thousands)
	Pre-2013 Activities
	Balance at December 31, 2012	$	243		$	1,084		$	1,327
	Change in estimate		—			(553	)		(553	)
	Cash payments		(243	)		(531	)		(774	)
	Balance at December 31, 2013	$	—		$	—		$	—
	2013 Activities
	Q3 2013 Activity:
	Provision	$	1,337		$	—		$	1,337
	Cash payments		(966	)		—			(966	)
	Balance at December 31, 2013		371			—			371
	Cash payments		(161	)		—			(161	)
	Balance at March 30, 2014		210			—			210
	Cash payments		—			—			—
	Balance at June 29, 2014		210			—			210
	Cash payments		—			—			—
	Balance at September 28, 2014	$	210		$	—		$	210
	Q4 2013 Activity:
	Provision	$	600		$	—		$	600
	Cash payments		(486	)		—			(486	)
	Balance at December 31, 2013		114			—			114
	Cash payments		(114	)		—			(114	)
	Balance at March 30, 2014	$	—		$	—		$	—
		Severance			Facility			Total
		and			Exit
		Benefits			Costs
		(in thousands)
	2014 Activities
	Q2 2014 Activity:
	Provision	$	572		$	—		$	572
	Cash payments		(530	)		—			(530	)
	Balance at June 29, 2014		42			—			42
	Cash payments		(42	)		—			(42	)
	Balance at September 28, 2014	$	—		$	—		$	—
	Q3 2014 Activity:
	Provision	$	225		$	—		$	225
	Cash payments		(225	)		—			(225	)
	Balance at September 28, 2014	$	—		$	—		$	—
	Balance at September 28, 2014	$	210		$	—		$	210

Retirement_Plans_Tables

Retirement Plans (Tables)	9 Months Ended
	Sep. 28, 2014
Postretirement Benefit Plans	'
Net Periodic Pension and Postretirement Cost (Benefit)	'
	For the three and nine months ended September 28, 2014 and September 29, 2013, Teradyne’s net periodic pension cost was comprised of the following:
		For the Three Months						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Service cost	$	761		$	871		$	2,368		$	2,557
	Interest cost		3,650			3,350			11,102			10,001
	Expected return on plan assets		(3,335	)		(3,664	)		(10,060	)		(10,925	)
	Amortization of unrecognized prior service cost		34			41			101			123
	Actuarial loss (gain)		—			—			362			(1,123	)
	Total net periodic pension cost	$	1,110		$	598		$	3,873		$	633
Defined Benefit Pension Plans	'
Net Periodic Pension and Postretirement Cost (Benefit)	'
	For the three and nine months ended September 28, 2014 and September 29, 2013, Teradyne’s net periodic postretirement benefit was comprised of the following:
		For the Three Months						For the Nine Months
		Ended						Ended
		September 28,			September 29,			September 28,			September 29,
		2014			2013			2014			2013
		(in thousands)
	Service cost	$	15		$	19		$	44		$	56
	Interest cost		84			86			252			257
	Amortization of unrecognized prior service benefit		(150	)		(150	)		(449	)		(449	)
	Actuarial gain		—			—			(247	)		(236	)
	Total net periodic post-retirement benefit	$	(51	)	$	(45	)	$	(400	)	$	(372	)

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 28, 2014
Segment Information	'
	Segment information is as follows:
			Semiconductor			Wireless			System			Corporate			Consolidated
			Test			Test			Test			and
												Eliminations
			(in thousands)
	Three months ended September 28, 2014:
	Net revenues		$	380,083		$	54,838		$	43,089		$	—		$	478,010
	Income before income taxes(1)(2)			91,900			2,379			5,779			612			100,670
	Three months ended September 29, 2013:
	Net revenues		$	304,131		$	93,132		$	36,113		$	—		$	433,376
	Income (loss) before income taxes(1)(2)			68,932			27,575			(2,462	)		(6,493	)		87,552
	Nine months ended September 28, 2014:
	Net revenues		$	1,063,254		$	144,747		$	116,586		$	—		$	1,324,587
	Income (loss) before income taxes(1)(2)			233,770			(8,477	)		5,512			(10,616	)		220,189
	Nine months ended September 29, 2013:
	Net revenues		$	808,068		$	226,116		$	108,448		$	—		$	1,142,632
	Income (loss) before income taxes(1)(2)			141,304			41,491			(153	)		(16,159	)		166,483
	-1	Pension and postretirement actuarial gains and losses, interest income, and interest expense and other are included in Corporate and Eliminations.
	-2	Included in the income (loss) before income taxes for each of the segments are charges and credits for the three and nine months ended September 28, 2014 and September 29, 2013 that include restructuring and other, and provision for excess and obsolete inventory, as follows:
Semiconductor Test	'
Schedule of Segment Reporting Information by Segment Charges	'
	Included in the Semiconductor Test segment are charges for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Cost of revenues—provision for excess and obsolete inventory		$	4,404		$	1,378		$	14,322		$	1,878
	Restructuring and other			—			282			—			416
	Total		$	4,404		$	1,660		$	14,322		$	2,294
Wireless Test	'
Schedule of Segment Reporting Information by Segment Charges	'
	Included in the Wireless Test segment are charges for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Cost of revenues—provision for excess and obsolete inventory		$	1,267		$	2,059		$	5,239		$	6,125
	Restructuring and other			—			—			426			82
	Total		$	1,267		$	2,059		$	5,665		$	6,207
System Test	'
Schedule of Segment Reporting Information by Segment Charges	'
	Included in the System Test segment are charges for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Cost of revenues—provision for excess and obsolete inventory		$	763		$	404		$	1,944		$	1,613
	Restructuring and other			225			1,055			371			1,430
	Total		$	988		$	1,459		$	2,315		$	3,043
Corporate And Eliminations	'
Schedule of Segment Reporting Information by Segment Charges	'
	Included in Corporate and Eliminations are credits for the following:
			For the Three Months						For the Nine Months
			Ended						Ended
			September 28,			September 29,			September 28,			September 29,
			2014			2013			2014			2013
			(in thousands)
	Restructuring and other		$	(630	)	$	(448	)	$	(630	)	$	(448	)
	Total		$	(630	)	$	(448	)	$	(630	)	$	(448	)

Schedule_of_Realized_Gains_and

Schedule of Realized Gains and (Losses) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Available For Sale Investment Securities Gross Realized Gain Losses [Line Items]	'	'	'	'
Realized gains	$986	$235	$1,677	$569
Realized (losses)	'	'	'	'

Schedule_of_Fair_Value_of_Fina

Schedule of Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail) (USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	$969,609	$857,960
U.S. Treasury Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	459,240	467,895
U.S. Government Agency Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	285,617	202,588
Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	99,774	105,598
Corporate Debt Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	94,357	65,387
Equity And Debt Mutual Funds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	12,099	13,156
Certificates of Deposit and Time Deposits	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	18,522	3,258
Non-U.S. Government Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	'	78
Fair Value, Measurements, Recurring	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Derivatives assets	'	153
Available for sale securities	1,181,313	'
Total including derivatives	1,181,313	1,199,751
Contingent consideration	1,600	2,230
Derivatives liabilities	546	'
Liabilities	2,146	2,230
Fair Value, Measurements, Recurring | Cash	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Cash and Cash equivalents	100,633	117,242
Fair Value, Measurements, Recurring | Cash Equivalents	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Cash and Cash equivalents	111,071	224,396
Fair Value, Measurements, Recurring | U.S. Treasury Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	459,240	467,895
Fair Value, Measurements, Recurring | U.S. Government Agency Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	285,617	202,588
Fair Value, Measurements, Recurring | Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	99,774	105,598
Fair Value, Measurements, Recurring | Corporate Debt Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	94,357	65,387
Fair Value, Measurements, Recurring | Equity And Debt Mutual Funds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	12,099	13,156
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	18,522	3,258
Fair Value, Measurements, Recurring | Non-U.S. Government Securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	'	78
Fair Value, Measurements, Recurring | Subtotal	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	'	1,199,598
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	'	'
Available for sale securities	212,711	'
Total including derivatives	212,711	296,263
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	100,633	117,242
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	99,979	165,865
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Fair Value, Measurements, Recurring | Equity And Debt Mutual Funds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	12,099	13,156
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Fair Value, Measurements, Recurring | Subtotal	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	'	296,263
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Derivatives assets	'	153
Available for sale securities	968,602	'
Total including derivatives	968,602	903,488
Derivatives liabilities	546	'
Liabilities	546	'
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	11,092	58,531
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	459,240	467,895
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	285,617	202,588
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	99,774	105,598
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	94,357	65,387
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	18,522	3,258
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	'	78
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Subtotal	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Available for sale securities	'	903,335
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Contingent consideration	1,600	2,230
Liabilities	$1,600	$2,230

Schedule_of_Reported_Financial

Schedule of Reported Financial Assets and Liabilities (Detail) (Fair Value, Measurements, Recurring, USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	$1,181,313	$1,199,751
Liabilities	2,146	2,230
Other Accrued Liabilities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Liabilities	546	'
Other current assets	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	'	153
Cash and Cash Equivalents	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	211,704	341,638
Marketable securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	594,801	586,882
Long-term marketable securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	374,808	271,078
Long-term other accrued liabilities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Liabilities	1,600	2,230
Quoted Prices in Active Markets for Identical Instruments (Level 1)	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	212,711	296,263
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	200,612	283,107
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	12,099	13,156
Significant Other Observable Inputs (Level 2)	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	968,602	903,488
Liabilities	546	'
Significant Other Observable Inputs (Level 2) | Other Accrued Liabilities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Liabilities	546	'
Significant Other Observable Inputs (Level 2) | Other current assets	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	'	153
Significant Other Observable Inputs (Level 2) | Cash and Cash Equivalents	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	11,092	58,531
Significant Other Observable Inputs (Level 2) | Marketable securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	594,801	586,882
Significant Other Observable Inputs (Level 2) | Long-term marketable securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Assets	362,709	257,922
Significant Unobservable Inputs (Level 3)	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Liabilities	1,600	2,230
Significant Unobservable Inputs (Level 3) | Long-term other accrued liabilities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'
Liabilities	$1,600	$2,230

Financial_Instruments_and_Deri2

Financial Instruments and Derivatives - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended	12 Months Ended
	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013	Dec. 31, 2013	Sep. 28, 2014	Dec. 31, 2013	Oct. 25, 2013
						Foreign Currency Forward Contracts	Foreign Currency Forward Contracts	ZTEC Instruments, Inc.
Financial Instruments and Fair Value [Line Items]	'	'	'	'	'	'	'	'
Contingent consideration	'	'	'	'	'	'	'	$2,200,000
Contingent consideration, maximum	'	'	'	'	'	'	'	5,000,000
Contingent consideration discount rate	'	'	5.20%	'	'	'	'	'
Changes to fair value of contingent consideration	630,000	'	630,000	'	'	'	'	'
Fair market value of investments with unrealized losses	212,156,000	'	212,156,000	'	241,760,000	'	'	'
Fair market value of investments with unrealized losses greater than one year	5,000,000	'	5,000,000	'	900,000	'	'	'
Fair market value of investments with unrealized losses less than one year	207,200,000	'	207,200,000	'	240,900,000	'	'	'
Notional amount of foreign currency forward contracts	'	'	'	'	'	67,900,000	74,800,000	'
Gains (losses) on foreign currency transactions	-400,000	-400,000	900,000	-5,000,000	'	-600,000	200,000	'
Offsetting foreign exchange contracts	0	'	0	'	0	'	'	'
Realized (losses) gains on foreign currency contracts	$200,000	$0	($1,600,000)	$4,100,000	'	'	'	'

Schedule_of_Changes_in_Fair_Va

Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Jun. 30, 2013	Mar. 31, 2013	Mar. 30, 2014	Dec. 31, 2013
Fair Value Measurements	'	'	'	'	'
Beginning Balance	$2,230	$75	$388	$2,230	$2,230
Fair value adjustment	-630	'	'	'	'
Contingent consideration payments	'	-75	-313	'	'
Ending Balance	$1,600	'	$75	$2,230	$2,230

Schedule_of_Carrying_Amounts_a

Schedule of Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $)	Sep. 28, 2014	Dec. 31, 2013		Sep. 29, 2013	Dec. 31, 2012	Mar. 31, 2009
In Thousands, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'		'	'	'
Cash and cash equivalents, Carrying Value	$211,704	$341,638		$572,868	$338,920	'
Marketable securities, Carrying Value	969,609	857,960		'	'	'
Convertible debt, Carrying Value	0	185,708		'	'	'
Japan loan, Carrying Value	'	'		'	'	10,000
Carrying Value	'	'		'	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'		'	'	'
Cash and cash equivalents, Carrying Value	211,704	341,638		'	'	'
Marketable securities, Carrying Value	969,609	857,960		'	'	'
Convertible debt, Carrying Value	'	185,708	[1]	'	'	'
Japan loan, Carrying Value	'	955		'	'	'
Fair Value	'	'		'	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'		'	'	'
Cash and cash equivalents, Fair Value	211,704	341,638		'	'	'
Marketable securities, Carrying Value	969,609	857,960		'	'	'
Convertible debt, Fair Value	'	611,433	[1]	'	'	'
Japan loan, Fair Value	'	$955		'	'	'
[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 feature.

Schedule_of_Available_for_Sale

Schedule of Available for Sale Marketable Securities (Detail) (USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	$965,843	$855,786
Available-for-sale marketable securities, Unrealized Gain	4,260	3,689
Available-for-sale marketable securities, Unrealized (Loss)	-494	-1,515
Available-for-sale marketable securities, Fair Market Value	969,609	857,960
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	212,156	241,760
U.S. Government Agency Securities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	285,528	202,573
Available-for-sale marketable securities, Unrealized Gain	195	75
Available-for-sale marketable securities, Unrealized (Loss)	-106	-60
Available-for-sale marketable securities, Fair Market Value	285,617	202,588
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	66,700	84,498
U.S. Treasury Securities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	458,958	468,084
Available-for-sale marketable securities, Unrealized Gain	373	94
Available-for-sale marketable securities, Unrealized (Loss)	-91	-283
Available-for-sale marketable securities, Fair Market Value	459,240	467,895
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	64,267	108,212
Commercial Paper	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	99,767	105,583
Available-for-sale marketable securities, Unrealized Gain	11	16
Available-for-sale marketable securities, Unrealized (Loss)	-4	-1
Available-for-sale marketable securities, Fair Market Value	99,774	105,598
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	23,722	7,993
Corporate Debt Securities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	92,883	65,747
Available-for-sale marketable securities, Unrealized Gain	1,734	762
Available-for-sale marketable securities, Unrealized (Loss)	-260	-1,122
Available-for-sale marketable securities, Fair Market Value	94,357	65,387
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	56,393	40,355
Equity And Debt Mutual Funds	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	10,199	10,463
Available-for-sale marketable securities, Unrealized Gain	1,933	2,742
Available-for-sale marketable securities, Unrealized (Loss)	-33	-49
Available-for-sale marketable securities, Fair Market Value	12,099	13,156
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	1,074	702
Certificates of Deposit and Time Deposits	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	18,508	3,258
Available-for-sale marketable securities, Unrealized Gain	14	'
Available-for-sale marketable securities, Fair Market Value	18,522	3,258
Non-U.S. Government Securities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	'	78
Available-for-sale marketable securities, Fair Market Value	'	$78

Schedule_of_Reported_Available

Schedule of Reported Available for Sale Marketable Securities (Detail) (USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	$965,843	$855,786
Available-for-sale marketable securities, Unrealized Gain	4,260	3,689
Available-for-sale marketable securities, Unrealized (Loss)	-494	-1,515
Available-for-sale marketable securities, Fair Market Value	969,609	857,960
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	212,156	241,760
Marketable securities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	594,500	586,818
Available-for-sale marketable securities, Unrealized Gain	319	85
Available-for-sale marketable securities, Unrealized (Loss)	-18	-21
Available-for-sale marketable securities, Fair Market Value	594,801	586,882
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	66,188	137,670
Long-term marketable securities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale marketable securities, Cost	371,343	268,968
Available-for-sale marketable securities, Unrealized Gain	3,941	3,604
Available-for-sale marketable securities, Unrealized (Loss)	-476	-1,494
Available-for-sale marketable securities, Fair Market Value	374,808	271,078
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	$145,968	$104,090

Contractual_Maturities_of_Inve

Contractual Maturities of Investments Held (Detail) (USD $)	Sep. 28, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities	'
Due within one year, cost	$594,500
Due after 1 year through 5 years, cost	330,340
Due after 5 years through 10 years, cost	5,772
Due after 10 years, cost	25,032
Total, cost	955,644
Due within one year, fair value	594,801
Due after 1 year through 5 years, fair value	330,412
Due after 5 years through 10 years, fair value	5,859
Due after 10 years, fair value	26,438
Total, fair value	$957,510

Schedule_of_Effect_of_Derivati

Schedule of Effect of Derivative Instruments in Statement of Operations Recognized (Detail) (USD $)	3 Months Ended	9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 28, 2014	Sep. 29, 2013	Dec. 31, 2013
Fair Value, Option, Quantitative Disclosures	'	'	'	'
Derivatives not designated as hedging instruments	$546	$546	'	$153
Foreign exchange contracts derivatives not designated as hedging instruments, Gains (Losses) Recognized in Statement of Operations	237	-1,632	4,068	'
Interest Expense and Other	'	'	'	'
Fair Value, Option, Quantitative Disclosures	'	'	'	'
Foreign exchange contracts derivatives not designated as hedging instruments, Gains (Losses) Recognized in Statement of Operations	237	-1,632	4,068	'
Not Designated as Hedging Instrument | Foreign Currency Forward Contracts | Other current assets	'	'	'	'
Fair Value, Option, Quantitative Disclosures	'	'	'	'
Derivatives asset not designated as hedging instruments	'	'	'	153
Not Designated as Hedging Instrument | Foreign Currency Forward Contracts | Other Accrued Liabilities	'	'	'	'
Fair Value, Option, Quantitative Disclosures	'	'	'	'
Derivatives liability not designated as hedging instruments	$546	$546	'	'

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended			9 Months Ended				0 Months Ended	1 Months Ended	9 Months Ended
	Mar. 31, 2009	Sep. 28, 2014	Mar. 30, 2014	Sep. 30, 2013	Sep. 28, 2014	Sep. 29, 2013	Dec. 31, 2013	Mar. 31, 2009	Mar. 13, 2014	Apr. 30, 2009	Sep. 28, 2014
									4.50% Convertible Senior Notes Due March 15, 2014	4.50% Convertible Senior Notes Due March 15, 2014	4.50% Convertible Senior Notes Due March 15, 2014
Debt Instrument	'	'	'	'	'	'	'	'	'	'	'
Borrowings from local bank	'	'	'	'	'	'	'	$10,000,000	'	'	'
Term of loan, years	'5 years	'	'	'	'	'	'	'	'	'	'
Debt instrument, interest rate, stated percentage	'	'	'	'	'	'	'	0.80%	'	4.50%	'
Loan collateralized by real estate mortgage	'	'	'	'	'	'	'	6,000,000	'	'	'
Unsecured loan	'	'	'	'	'	'	'	4,000,000	'	'	'
Semiannual principal payments of loan	'	'	1,000,000	1,000,000	'	'	'	'	'	'	'
Aggregate principal amount	'	0	'	'	0	'	189,998,000	'	'	190,000,000	'
Initial debt conversion price	'	'	'	'	'	'	'	'	'	$5.47	'
Conversion rate in number of shares	'	'	'	'	'	'	'	'	'	182.65	131.95
Additional aggregate principal amount	'	'	'	'	'	'	'	'	'	1,000	'
Senior notes maturity date	'	'	'	'	'	'	'	'	'	15-Mar-14	'
Number of shares excluded for conversion rate calculation	'	'	'	'	'	'	'	'	'	'	50.7
Trading days used to determine average price per share	'	'	'	'	'	'	'	'	'	'	'25 days
Average trading price of common shares	'	'	'	'	'	'	'	'	'	'	$19.74
Payments of long-term debt	'	'	'	'	$190,975,000	$1,063,000	'	'	'	'	$190,000,000
Stock issued in conversion of notes	'	'	'	'	'	'	'	'	'	'	25,100,000
Stock received and retired	'	'	'	'	'	'	'	'	25,100,000	'	'
Common stock shares were issued for warrants exercised	'	19,300,000	'	'	21,200,000	'	'	'	'	'	'
Strike price per share of warrant	'	$7.63	'	'	$7.64	'	'	'	'	'	'

Components_of_Convertible_Seni

Components of Convertible Senior Notes (Detail) (USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt Instrument	'	'
Debt principal	$0	$189,998
Unamortized debt discount	0	4,290
Net carrying amount of the convertible debt	$0	$185,708

Interest_Expense_on_Convertibl

Interest Expense on Convertible Senior Notes (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Debt Instrument	'	'	'	'
Contractual interest expense	$0	$2,114	$1,757	$6,388
Amortization of the discount component and debt issue fees	0	4,221	4,493	12,266
Total interest expense on the convertible debt	$0	$6,335	$6,250	$18,654

Schedule_of_Prepayments_Detail

Schedule of Prepayments (Detail) (USD $)	Sep. 28, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Prepaid Expenses [Line Items]	'	'
Contract manufacturer prepayments	$68,126	$115,388
Prepaid maintenance and other services	6,794	6,538
Prepaid taxes	3,413	3,281
Other prepayments	10,399	11,167
Prepayments	$88,732	$136,374

Deferred_Revenue_and_Customer_2

Deferred Revenue and Customer Advances (Detail) (USD $)	Sep. 28, 2014	Jun. 29, 2014	Dec. 31, 2013	Sep. 29, 2013	Jun. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Deferred Revenue Arrangement	'	'	'	'	'	'
Extended warranty	$43,497	$40,052	$34,909	$36,320	$34,854	$26,987
Equipment maintenance and training	27,703	'	22,455	'	'	'
Customer advances	5,041	'	4,825	'	'	'
Undelivered elements	7,185	'	6,971	'	'	'
Total deferred revenue and customer advances	$83,426	'	$69,160	'	'	'

Warranty_Accrual_Included_in_O

Warranty Accrual Included in Other Accrued Liabilities (Detail) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Schedule of Accrued Liabilities [Line Items]	'	'	'	'
Balance at beginning of period	$9,073	$7,351	$6,660	$9,786
Accruals for warranties issued during the period	4,419	3,674	12,675	8,781
Adjustments related to pre-existing warranties	-559	-524	-1,000	-2,323
Settlements made during the period	-2,982	-2,470	-8,384	-8,213
Balance at end of period	$9,951	$8,031	$9,951	$8,031

Extended_Product_Warranty_Incl

Extended Product Warranty Included in Short and Long-Term Deferred Revenue and Customer Advances (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Schedule of Accrued Liabilities [Line Items]	'	'	'	'
Balance at beginning of period	$40,052	$34,854	$34,909	$26,987
Deferral of new extended warranty revenue	9,896	5,586	24,218	17,791
Recognition of extended warranty deferred revenue	-6,451	-4,120	-15,630	-8,458
Balance at end of period	$43,497	$36,320	$43,497	$36,320

Stock_Based_Compensation_Addit

Stock Based Compensation - Additional Information (Detail) (USD $)

1 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

1 Months Ended

Share data in Millions, except Per Share data, unless otherwise specified

Jan. 31, 2014

Sep. 28, 2014

Sep. 29, 2013

Sep. 28, 2014

Sep. 29, 2013

Sep. 28, 2014

Sep. 28, 2014

Jan. 24, 2014

Jan. 31, 2014

Sep. 28, 2014

Jan. 24, 2014

Jan. 31, 2014

Jan. 31, 2014

Service-Based Restricted Stock Units

Service-Based Restricted Stock Units

Restricted Stock Units

Stock Options

Stock Options

TSR Performance-Based Restricted Stock Units

TSR Performance-Based Restricted Stock Units

TSR Performance-Based Restricted Stock Units

TSR Performance-Based Restricted Stock Units

TSR Performance-Based Restricted Stock Units

Employees

Maximum

Minimum

Share-based Compensation Arrangement by Share-based Payment Award

'

'

'

'

'

'

'

'

'

'

'

'

'

Restricted stock unit awards to employees

'

'

'

1.7

1.9

'

'

'

0.1

0.1

'

'

'

Total shareholder return performance measurement period

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

Percentage of vesting of target shares upon performance achieved

'

'

'

'

'

'

'

'

'

'

'

200.00%

0.00%

Weighted average grant date fair value of restricted stock units granted

'

'

'

$19.09

$16.60

'

'

'

'

$22.06

'

'

'

Estimated annual dividend amount per share

'

'

'

'

'

'

$0.24

'

'

$0.24

'

'

'

Stock price

'

'

'

'

'

'

'

$19.16

'

'

$19.16

'

'

Number of service-based stock options granted to executive officers

'

0.1

0.2

'

'

'

'

'

'

'

'

'

'

Weighted average grant date fair value of stock options granted to executive officers

'

$5.49

$6.09

'

'

'

'

'

'

'

'

'

'

Period of stock granted to employees and executive officers vest in equal installments

'

'

'

'

'

'4 years

'4 years

'

'

'

'

'

'

Stock options term

'

'7 years

'

'

'

'

'

'

'

'

'

'

'

Stock based compensation expense related to retirement agreement

$6,600,000

'

'

'

'

'

'

'

'

'

'

'

'

Schedule_of_Estimated_Fair_Val

Schedule of Estimated Fair Value of TSR Performance-Based Restricted Stock Unit Awards Assumptions (Detail) (TSR Performance-Based Restricted Stock Units)	9 Months Ended
	Sep. 28, 2014
TSR Performance-Based Restricted Stock Units	'
Share-based Compensation Arrangement by Share-based Payment Award	'
Risk-free interest rate	0.75%
Teradyne volatility-historical	36.10%
Philadelphia Semiconductor Index volatility-historical	24.60%
Dividend yield	1.25%

Schedule_of_Estimated_Fair_Val1

Schedule of Estimated Fair Value of Stock Options Assumptions (Detail) (Stock Options)	9 Months Ended
	Sep. 28, 2014	Sep. 29, 2013
Stock Options	'	'
Share-based Compensation Arrangement by Share-based Payment Award	'	'
Expected life (years)	'4 years	'4 years
Risk-free interest rate	1.20%	0.60%
Volatility-historical	38.80%	46.80%
Dividend yield	1.25%	0.00%

Changes_in_Accumulated_Other_C

Changes in Accumulated Other Comprehensive Income Balances (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning balance	'	'	$4,000	'
Other comprehensive income before reclassifications, net of tax	'	'	2,166	'
Amounts reclassified from accumulated other comprehensive income, net of tax	-712	-258	-1,307	-608
Other comprehensive income (loss)	-850	365	859	-1,248
Ending balance	4,859	'	4,859	'
Unrealized Gains on Marketable Securities	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning balance	'	'	1,381	'
Other comprehensive income before reclassifications, net of tax	'	'	2,166	'
Amounts reclassified from accumulated other comprehensive income, net of tax	'	'	-1,086	'
Other comprehensive income (loss)	'	'	1,080	'
Ending balance	2,461	'	2,461	'
Retirement Plans Prior Service Benefit	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning balance	'	'	2,619	'
Amounts reclassified from accumulated other comprehensive income, net of tax	'	'	-221	'
Other comprehensive income (loss)	'	'	-221	'
Ending balance	$2,398	'	$2,398	'

Changes_in_Accumulated_Other_C1

Changes in Accumulated Other Comprehensive Income Balances (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'
Other comprehensive income before reclassifications, tax	($139)	$358	$1,103	($367)	'
Other comprehensive income before reclassifications, tax	'	'	0	'	'
Amounts reclassified from accumulated other comprehensive income, tax	-348	-109	-591	-231	'
Amounts reclassified from accumulated other comprehensive income, tax	-42	-40	-127	-119	'
Unrealized gains on marketable securities, tax	1,306	'	1,306	'	794
Retirement plans prior service benefit, tax	-411	'	-411	'	-284
Unrealized Gains on Marketable Securities	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'
Other comprehensive income before reclassifications, tax	'	'	1,103	'	'
Amounts reclassified from accumulated other comprehensive income, tax	'	'	-591	'	'
Retirement Plans Prior Service Benefit	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'
Other comprehensive income before reclassifications, tax	'	'	0	'	'
Amounts reclassified from accumulated other comprehensive income, tax	'	'	($127)	'	'

Reclassification_Out_of_Accumu

Reclassification Out of Accumulated Other Comprehensive Income to Statement of Operations (Detail) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014		Sep. 29, 2013		Sep. 28, 2014		Sep. 29, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'		'		'		'
Unrealized gains	$638		$189		$1,086		$401
Prior service benefit	74	[1]	69	[1]	221	[1]	207	[1]
Total reclassifications	$712		$258		$1,307		$608
[1]	The amortization of prior service benefit is included in the computation of net periodic pension cost and postretirement benefit; see Note N: "Retirement Plans."

Reclassification_Out_of_Accumu1

Reclassification Out of Accumulated Other Comprehensive Income to Statement of Operations (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Unrealized gains, tax	$348	$109	$591	$231
Prior service benefit, tax	$42	$40	$127	$119

Schedule_of_Amortizable_Intang

Schedule of Amortizable Intangible Assets (Detail) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets	'	'
Gross Carrying Amount	$513,972	$515,464
Accumulated Amortization	316,495	263,173
Net Carrying Amount	197,477	252,291
Weighted Average Useful Life, years	'6 years 10 months 24 days	'6 years 10 months 24 days
Developed technology	'	'
Finite-Lived Intangible Assets	'	'
Gross Carrying Amount	342,933	342,933
Accumulated Amortization	212,949	174,563
Net Carrying Amount	129,984	168,370
Weighted Average Useful Life, years	'6 years 2 months 12 days	'6 years 2 months 12 days
Customer Relationships	'	'
Finite-Lived Intangible Assets	'	'
Gross Carrying Amount	141,005	141,497
Accumulated Amortization	90,244	76,963
Net Carrying Amount	50,761	64,534
Weighted Average Useful Life, years	'8 years	'8 years
Trade names and trademarks	'	'
Finite-Lived Intangible Assets	'	'
Gross Carrying Amount	30,034	30,034
Accumulated Amortization	13,302	10,647
Net Carrying Amount	16,732	19,387
Weighted Average Useful Life, years	'9 years 1 month 6 days	'9 years 1 month 6 days
Customer backlog	'	'
Finite-Lived Intangible Assets	'	'
Gross Carrying Amount	'	1,000
Accumulated Amortization	'	$1,000
Weighted Average Useful Life, years	'	'4 months 24 days

Intangible_Assets_Additional_I

Intangible Assets - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Goodwill and Intangible Assets Disclosure [Line Items]	'	'	'	'
Aggregate intangible asset amortization expense	$18,271	$18,064	$54,813	$54,163

Schedule_of_Estimated_Intangib

Schedule of Estimated Intangible Asset Amortization Expense (Detail) (USD $)	Sep. 28, 2014
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets	'
2014 (remainder)	$15,327
2015	53,391
2016	53,391
2017	47,232
2018	22,691
Thereafter	$5,445

Computation_of_Basic_and_Dilut

Computation of Basic and Diluted Net Income Per Common Share (Detail) (USD $)	3 Months Ended				9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 28, 2014		Sep. 29, 2013		Sep. 28, 2014		Sep. 29, 2013
Net Income Loss Per Common Share	'		'		'		'
Net income for basic and diluted net income per share	$82,949		$69,459		$185,083		$142,604
Weighted average common shares-basic	207,381		191,307		198,367		190,521
Incremental shares from assumed conversion of convertible notes	'		23,257	[1]	6,684	[1]	23,303	[1]
Convertible note hedge warrant shares	8,885	[2]	18,678	[2]	16,744	[2]	18,742	[2]
Employee stock purchase rights	21		19		28		35
Dilutive potential common shares	10,952		44,521		25,428		44,644
Weighted average common shares-diluted	218,333		235,828		223,795		235,165
Net income per common share-basic	$0.40		$0.36		$0.93		$0.75
Net income per common share-diluted	$0.38		$0.29		$0.83		$0.61
Restricted Stock Units	'		'		'		'
Net Income Loss Per Common Share	'		'		'		'
Incremental shares attributable to share based payment arrangements	1,167		1,102		975		1,000
Stock Option	'		'		'		'
Net Income Loss Per Common Share	'		'		'		'
Incremental shares attributable to share based payment arrangements	879		1,465		997		1,564
[1]	Incremental shares from conversion of the convertible notes for the nine months ended September 28, 2014 were calculated using the difference between the average Teradyne stock price from January 1, 2014 through March 12, 2014 and the conversion price of $5.4750, multiplied by 34.7 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 from January 1, 2014 to March 12, 2014 and adjusted for the number of days the convertible notes were outstanding. Incremental shares from assumed conversion of the convertible notes for the three and nine months ended September 29, 2013 were calculated using the difference between the average Teradyne stock price for the period the convertible notes were outstanding and the conversion price of $5.48, multiplied by the 34.7 million shares to be issued upon conversion. 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 note hedge warrant shares for the three and nine months ended September 28, 2014 are calculated using the difference between the average Teradyne stock price for the period the warrants were outstanding and the warrant price of $7.63 and $7.64, respectively, multiplied by the weighted average warrant shares outstanding. The result of this calculation, representing the total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period the warrants were outstanding. Convertible note hedge warrant shares for the three and nine months ended September 29, 2013 are calculated using the difference between the average Teradyne stock price for the period and the warrant price of $7.67, multiplied by the 34.7 million shares that would be issued upon conversion. The result of this calculation, representing the total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period.

Computation_of_Basic_and_Dilut1

Computation of Basic and Diluted Net Income Per Common Share (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 29, 2013	Sep. 30, 2013	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 28, 2014	Sep. 30, 2013
					Convertible Notes	Convertible Notes	Convertible Notes Hedge Warrant	Convertible Notes Hedge Warrant	Convertible Notes Hedge Warrant
Net Income Loss Per Common Share	'	'	'	'	'	'	'	'	'
Initial debt conversion price	'	'	'	'	$5.47	$5.48	'	'	$7.67
Shares that would be issued upon conversion	34.7	34.7	34.7	34.7	'	'	'	'	'
Initial debt conversion price	'	'	'	'	'	'	$7.63	$7.64	'

Net_Income_Per_Common_Share_Ad

Net Income Per Common Share - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 30, 2013	Sep. 28, 2014	Sep. 29, 2013
Net Income Loss Per Common Share	'	'	'	'	'
Shares that would be issued upon conversion	'	34.7	34.7	34.7	34.7
Exercise of stock options	0.3	0.4	'	0.3	0.4
Convertible Notes Hedge Warrant	'	'	'	'	'
Net Income Loss Per Common Share	'	'	'	'	'
Initial debt conversion price	'	'	7.67	'	'

Restructuring_and_Other_Additi

Restructuring and Other - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended		9 Months Ended
	Sep. 28, 2014	Sep. 28, 2014	Sep. 28, 2014	Sep. 28, 2014	Sep. 29, 2013	Sep. 29, 2013	Sep. 29, 2013	Sep. 29, 2013
			Severance and Benefits	Wireless Test	System Test and Semiconductor Test	System Test	Semiconductor Test	Corporate And Eliminations
				Employee	Employee
Restructuring Cost and Reserve	'	'	'	'	'	'	'	'
Severance benefit and charges	'	'	'	$800,000	$1,500,000	$1,400,000	$400,000	'
Reduction in employees head count	'	'	'	30	40	'	'	'
Change in estimated exit costs related to leased facility	'	'	'	'	'	'	'	-400,000
Accrual balance for severance and benefits	210,000	210,000	210,000	'	'	'	'	'
Changes to fair value of contingent consideration	$630,000	$630,000	'	'	'	'	'	'

Schedule_of_Restructuring_and_

Schedule of Restructuring and Other Net (Detail) (USD $)

Sep. 28, 2014

Mar. 30, 2014

Dec. 31, 2013

Sep. 28, 2014

Jun. 29, 2014

Mar. 30, 2014

Dec. 31, 2013

Sep. 28, 2014

Jun. 29, 2014

Sep. 28, 2014

Dec. 31, 2013

Sep. 28, 2014

Mar. 30, 2014

Dec. 31, 2013

Sep. 28, 2014

Jun. 29, 2014

Mar. 30, 2014

Dec. 31, 2013

Sep. 28, 2014

Jun. 29, 2014

Sep. 28, 2014

Dec. 31, 2013

Dec. 31, 2013

In Thousands, unless otherwise specified

Q3 2013 Activity

Q3 2013 Activity

Q3 2013 Activity

Q3 2013 Activity

Q4 2013 Activity

Q4 2013 Activity

Q2 2014 Activity

Q2 2014 Activity

Q3 2014 Activity

Pre-2013 Activities

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Severance and Benefits

Facility Exit Costs

Q3 2013 Activity

Q3 2013 Activity

Q3 2013 Activity

Q3 2013 Activity

Q4 2013 Activity

Q4 2013 Activity

Q2 2014 Activity

Q2 2014 Activity

Q3 2014 Activity

Pre-2013 Activities

Pre-2013 Activities

Restructuring Cost and Reserve

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Beginning Balance

$210

$371

'

$210

$210

$114

'

$42

'

'

$1,327

$210

$371

'

$210

$210

$114

'

$42

'

'

$243

$1,084

Provision

'

'

1,337

'

'

'

600

'

572

225

'

'

'

1,337

'

'

'

600

'

572

225

'

'

Change in estimate

'

'

'

'

'

'

'

'

'

'

-553

'

'

'

'

'

'

'

'

'

'

'

-553

Cash payments

'

-161

-966

'

'

-114

-486

-42

-530

-225

-774

'

-161

-966

'

'

-114

-486

-42

-530

-225

-243

-531

Ending balance

$210

$210

$371

$210

$210

'

$114

'

$42

'

$0

$210

$210

$371

$210

$210

'

$114

'

$42

'

$0

$0

Retirement_Plans_Additional_In

Retirement Plans - Additional Information (Detail) (USD $)	9 Months Ended	0 Months Ended	9 Months Ended
	Sep. 29, 2013	Oct. 27, 2014	Sep. 28, 2014	Sep. 28, 2014
		Subsequent Event	U.S. Supplemental Executive Defined Benefit Pension Plan	Foreign Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure	'	'	'	'
Actuarial loss (gain)	$1,359,000	$50,000,000	'	'
Contribution to defined benefit pension plans	'	'	$1,300,000	$1,200,000

Schedule_of_Net_Periodic_Pensi

Schedule of Net Periodic Pension and Postretirement Cost (Benefit) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Defined Benefit Plan Disclosure	'	'	'	'
Actuarial gain	'	'	'	($1,359)
Defined Benefit Pension Plans	'	'	'	'
Defined Benefit Plan Disclosure	'	'	'	'
Service cost	761	871	2,368	2,557
Interest cost	3,650	3,350	11,102	10,001
Expected return on plan assets	-3,335	-3,664	-10,060	-10,925
Amortization of unrecognized prior service benefit	34	41	101	123
Actuarial gain	'	'	362	-1,123
Total net periodic pension cost	1,110	598	3,873	633
Postretirement Benefit Plans	'	'	'	'
Defined Benefit Plan Disclosure	'	'	'	'
Service cost	15	19	44	56
Interest cost	84	86	252	257
Amortization of unrecognized prior service benefit	-150	-150	-449	-449
Actuarial gain	'	'	-247	-236
Total net periodic pension cost	($51)	($45)	($400)	($372)

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 28, 2014
Purchase Commitment, Excluding Long-term Commitment	'
Aggregate purchase commitments	155.2
Purchase commitments less than one year	147.4
Maximum	'
Purchase Commitment, Excluding Long-term Commitment	'
Purchase commitments period	'1 year

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013	Dec. 31, 2013
Income Taxes [Line Items]	'	'	'	'	'
Effective tax rate	18.00%	21.00%	16.00%	14.00%	'
U.S. statutory federal tax rate	'	'	35.00%	'	'
Uncertain tax positions	$31.60	'	$31.60	'	$21.20
Net increase in uncertain tax positions	'	'	10.4	'	'
Decrease in uncertain tax position resulting from expiration of statutes of limitations	'	'	2.8	'	'
Tax savings due to the tax holiday	'	'	$12.30	'	'
Tax savings due to the tax holiday, per share	'	'	$0.05	'	'
Tax holiday expiration date	'	'	'December 31, 2015	'	'

Schedule_of_Segment_Informatio

Schedule of Segment Information (Detail) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014		Sep. 29, 2013		Sep. 28, 2014		Sep. 29, 2013
Segment Reporting Information [Line Items]	'		'		'		'
Net revenues	$478,010		$433,376		$1,324,587		$1,142,632
Income (loss) before income taxes	100,670	[1],[2]	87,552	[1],[2]	220,189	[1],[2]	166,483	[1],[2]
Semiconductor Test	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Net revenues	380,083		304,131		1,063,254		808,068
Income (loss) before income taxes	91,900	[1],[2]	68,932	[1],[2]	233,770	[1],[2]	141,304	[1],[2]
Wireless Test	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Net revenues	54,838		93,132		144,747		226,116
Income (loss) before income taxes	2,379	[1],[2]	27,575	[1],[2]	-8,477	[1],[2]	41,491	[1],[2]
System Test	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Net revenues	43,089		36,113		116,586		108,448
Income (loss) before income taxes	5,779	[1],[2]	-2,462	[1],[2]	5,512	[1],[2]	-153	[1],[2]
Corporate And Eliminations	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Income (loss) before income taxes	$612	[1],[2]	($6,493)	[1],[2]	($10,616)	[1],[2]	($16,159)	[1],[2]
[1]	Pension and postretirement actuarial gains and losses, interest income, and interest expense and other are included in Corporate and Eliminations.
[2]	Included in the income (loss) before income taxes for each of the segments are charges and credits for the three and nine months ended September 28, 2014 and September 29, 2013 that include restructuring and other, and provision for excess and obsolete inventory, as follows:

Schedule_of_Segment_Reporting_

Schedule of Segment Reporting Information by Segment Charges (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Segment Reporting Information [Line Items]	'	'	'	'
Restructuring and other	($405)	$889	$167	$1,480
Semiconductor Test	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Cost of revenues-provision for excess and obsolete inventory	4,404	1,378	14,322	1,878
Restructuring and other	'	282	'	416
Total	4,404	1,660	14,322	2,294
System Test	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Cost of revenues-provision for excess and obsolete inventory	763	404	1,944	1,613
Restructuring and other	225	1,055	371	1,430
Total	988	1,459	2,315	3,043
Wireless Test	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Cost of revenues-provision for excess and obsolete inventory	1,267	2,059	5,239	6,125
Restructuring and other	'	'	426	82
Total	1,267	2,059	5,665	6,207
Corporate And Eliminations	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Restructuring and other	-630	-448	-630	-448
Total	($630)	($448)	($630)	($448)

Shareholders_Equity_Additional

Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended	9 Months Ended		47 Months Ended
Share data in Millions, except Per Share data, unless otherwise specified	Aug. 31, 2014	Jan. 31, 2014	Sep. 28, 2014	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Nov. 30, 2010
							Maximum
Stockholders Equity Note Disclosure [Line Items]	'	'	'	'	'	'	'
Stock repurchase program, authorized amount	'	'	'	'	'	'	$200,000,000
Repurchase of stock, shares	'	'	0	'	0	2.6	'
Repurchase of stock, value	'	'	'	'	'	31,200,000	'
Common stock average price	'	'	'	'	'	$11.84	'
Dividends payable, amount per share	$0.06	$0.06	'	'	'	'	'
Dividends payable, date to be paid	26-Sep-14	2-Jun-14	'	'	'	'	'
Dividends payable, record date	5-Sep-14	9-May-14	'	'	'	'	'
Dividend payment	'	'	$12,800,000	$24,428,000	'	'	'

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (Subsequent Event, Avionics Interface Technologies, LLC, USD $)	1 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2014
Subsequent Event | Avionics Interface Technologies, LLC	'
Subsequent Event [Line Items]	'
Acquisition price	$18.90
Contingent consideration, maximum	$2.10