Debt (Narrative) (Details) (USD $)	1 Months Ended	6 Months Ended
	Mar. 31, 2009	Jul. 03, 2011	Jun. 30, 2011	Dec. 31, 2010	Mar. 31, 2009 4.50% Convertible Senior Notes Due March 15, 2014 [Member]	Jul. 03, 2011 Convertible Senior Notes [Member]	Apr. 01, 2009 Convertible Senior Notes [Member]	Mar. 31, 2009 Convertible Notes Hedge And Warrant [Member]	Jul. 03, 2011 Short-Term Debt [Member]	Jul. 03, 2011 Long-Term Debt [Member]
Borrowings from local bank	$ 10,000,000
Term of loan, years	5
Loan collateralized by real estate mortgage	6,000,000
Unsecured loan	4,000,000
Semiannual principal payments of loan		1,000,000
Outstanding loan principal amount									2,500,000	4,900,000
Aggregate principal amount		190,000,000		190,000,000			190,000,000
Debt instrument, interest rate, stated percentage	0.81%				4.50%
Senior notes maturity date	March 15, 2014
Additional aggregate principal amount			1,000
Initial conversion rate			The Notes may be converted, under certain circumstances and during certain periods, at an initial conversion rate of approximately 182.65 shares of Teradyne's common stock per $1,000 principal amount of Notes, which is equivalent to an initial conversion price of approximately $5.48, a 25% conversion premium based on the last reported sale price of $4.38 per share of Teradyne's common stock on March 31, 2009.
Initial debt conversion price	$ 5.48	$ 5.48						$ 7.67
Last reported sale price of debt	$ 4.38
Debt conversion premium percentage	25.00%
Antidilution adjustments, shares		34,703,196
Convertible note hedges		64,600,000
Strike price of warrant	7.67
Percentage of warrant price in excess of closing price of common stock	75.00%
Warrants conversion premium percentage	75.00%
Unamortized debt discount		40,127,000		45,941,000		40,100,000
Amortization period of unamortized discount, years		2.75
Carrying amount of equity component		63,400,000
Conversion value of notes		$ 526,800,000