Schedule of Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 27, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 361,666	$ 211,596
Available-for-sale marketable securities, Unrealized Gain	8,284	4,687
Available-for-sale marketable securities, Unrealized (Loss)	(87)	(262)
Available-for-sale marketable securities, Fair Market Value	369,863	216,021
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	24,431	23,999
U.S. Treasury Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	201,193	42,167
Available-for-sale marketable securities, Unrealized Gain	1,606	431
Available-for-sale marketable securities, Unrealized (Loss)	(33)	(216)
Available-for-sale marketable securities, Fair Market Value	202,766	42,382
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	20,611	17,556
Commercial Paper
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	102,141	54,124
Available-for-sale marketable securities, Unrealized Gain	8	26
Available-for-sale marketable securities, Unrealized (Loss)	0	(1)
Available-for-sale marketable securities, Fair Market Value	102,149	54,149
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	500	1,391
Corporate Debt Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	44,350	93,267
Available-for-sale marketable securities, Unrealized Gain	6,417	4,081
Available-for-sale marketable securities, Unrealized (Loss)	(52)	(41)
Available-for-sale marketable securities, Fair Market Value	50,715	97,307
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	2,207	2,009
Certificates of Deposit and Time Deposits
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	2,414	4,751
Available-for-sale marketable securities, Unrealized Gain	2
Available-for-sale marketable securities, Unrealized (Loss)	0
Available-for-sale marketable securities, Fair Market Value	2,416	4,751
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	0
U.S. Government Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	4,288	9,942
Available-for-sale marketable securities, Unrealized Gain	60	14
Available-for-sale marketable securities, Unrealized (Loss)	(2)	(4)
Available-for-sale marketable securities, Fair Market Value	4,346	9,952
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	1,113	3,043
Debt Mutual Funds
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	6,661	6,753
Available-for-sale marketable securities, Unrealized Gain	191	135
Available-for-sale marketable securities, Fair Market Value	6,852	6,888
Non-U.S. Government Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	619	592
Available-for-sale marketable securities, Fair Market Value	$ 619	$ 592

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=ter_DebtMutualFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ForeignCorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: