Debt - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended		1 Months Ended		9 Months Ended
	Mar. 31, 2009 Y	Sep. 30, 2012 D	Sep. 30, 2012	Dec. 31, 2011	Apr. 30, 2009 4.50% Convertible Senior Notes	Mar. 31, 2009 4.50% Convertible Senior Notes	Sep. 30, 2012 4.50% Convertible Senior Notes	Oct. 02, 2011 Convertible Notes Hedge Warrant	Sep. 30, 2012 Convertible Notes Hedge Warrant	Mar. 31, 2009 Convertible Notes Hedge Warrant	Sep. 30, 2012 Convertible Senior Notes	Sep. 30, 2012 Current Debt	Sep. 30, 2012 Long-term Debt
Debt Instrument
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												3,900,000	1,300,000
Aggregate principal amount		190,000,000	190,000,000	190,000,000	190,000,000
Senior notes maturity date					March 15, 2014
Initial conversion rate in number of shares							182.65
Additional aggregate principal amount							1,000
Initial debt conversion price		$ 5.48	$ 5.48			$ 5.48			$ 7.67	$ 7.67
Debt conversion premium percentage						25.00%
Last reported sale price per share of debt						$ 4.38
Initial conversion rate			The Notes may be converted, at the option of the holder, 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.
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		23,732,000	23,732,000	33,902,000							23,700,000
Amortization period of unamortized discount, years			1 year 6 months
Carrying amount of equity component		63,400,000	63,400,000
If-converted value of notes			$ 493,500,000