Debt (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended				0 Months Ended	1 Months Ended			3 Months Ended
	Mar. 31, 2009 Y	Apr. 01, 2012 D	Dec. 31, 2011	Apr. 01, 2012 Current Debt [Member]	Apr. 01, 2012 Long-Term Debt [Member]	Oct. 02, 2011 4.50% Convertible Senior Notes [Member]	Apr. 30, 2009 4.50% Convertible Senior Notes [Member]	Mar. 31, 2009 4.50% Convertible Senior Notes [Member]	Apr. 01, 2012 Convertible Senior Notes [Member]	Apr. 03, 2011 Convertible Notes Hedge Warrant [Member]	Apr. 01, 2012 Convertible Notes Hedge Warrant [Member]	Mar. 31, 2009 Convertible Notes Hedge Warrant [Member]
Debt Instrument [Line Items]
Borrowings from local bank	$ 10,000,000
Term of loan, years	5
Debt instrument, interest rate, stated percentage	0.81%						4.50%
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				2,400,000	2,400,000
Aggregate principal amount		190,000,000	190,000,000				190,000,000
Senior notes maturity date							March 15, 2014
Additional aggregate principal amount						1,000
Initial conversion rate in number of shares						182.65
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	$ 7.67
Last reported sale price per share of debt								$ 4.38
Debt conversion premium percentage								25.00%
Conversion of common stock for trading days, number of days		20
Consecutive trading days		30
Percent of increase in conversion price		130.00%
Antidilution adjustments, shares		34,703,196								34,700,000
Convertible note hedges		64,600,000
Strike price per share of warrant	$ 7.67
Percentage of warrant price in excess of closing price of common stock	75.00%
Proceeds from warrants	43,000,000
Warrants conversion premium percentage	75.00%
Unamortized discount		30,627,000	33,902,000						30,600,000
Amortization period of unamortized discount, years		2.0
Carrying amount of equity component		63,400,000
If-converted value of notes		$ 586,100,000