Computation of Basic and Diluted Net (Loss) Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2019	[1],[2]	Sep. 29, 2019	[3]	Jun. 30, 2019	[4]	Mar. 31, 2019	[5]	Dec. 31, 2018	[6],[7]	Sep. 30, 2018	[8]	Jul. 01, 2018	[9]	Apr. 01, 2018	[10]	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Income Loss Per Common Share
Net income for basic and diluted net income per share		$ 125,075		$ 135,860		$ 97,397		$ 109,138		$ 143,790		$ 119,978		$ 101,037		$ 86,974		$ 467,468	$ 451,779	$ 257,692
Weighted average common shares-basic																		170,425	187,672	198,069
Incremental shares from assumed conversion of convertible notes	[11]																	4,909	2,749	1,298
Convertible note hedge warrant shares	[12]																	2,698	485	112
Employee stock purchase plan																		13	36	27
Dilutive potential common shares																		9,034	4,933	3,572
Weighted average common shares-diluted																		179,459	192,605	201,641
Net income per common share-basic		$ 0.75		$ 0.80		$ 0.57		$ 0.63		$ 0.80		$ 0.65		$ 0.53		$ 0.45		$ 2.74	$ 2.41	$ 1.30
Net income per common share-diluted		$ 0.69		$ 0.75		$ 0.55		$ 0.62		$ 0.79		$ 0.63		$ 0.52		$ 0.43		$ 2.60	$ 2.35	$ 1.28
Restricted Stock Units
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements																		1,236	1,385	1,800
Stock Options
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements																		178	278	335

[1] Restructuring and other includes a $5.8 million gain for the decrease in the fair value adjustment to the MiR acquisition contingent consideration, partially offset by a $3.0 million fair value adjustment to increase the AutoGuide acquisition contingent consideration, $0.5 million of employee severance charges and $0.2 million of acquisition related expenses and compensation.

[2] Teradyne recorded pension and post retirement net actuarial losses of $7.7 million for the fourth quarter in 2019. See Note B: “Accounting Policies” for a discussion of Teradyne’s accounting policy.

[3] Restructuring and other includes a $7.8 million gain for the decrease in the fair value of MiR contingent consideration liability, partially offset by $0.8 million of employee severance charges and $0.5 million of acquisition related expenses and compensation.

[4] Restructuring and other includes a $11.7 million gain for the decrease in the fair value of the MiR contingent consideration liability, partially offset by $0.8 million of employee severance charges and $0.5 million of acquisition related expenses and compensation.

[5] Restructuring and other includes a $3.0 million fair value adjustment to increase the MiR acquisition contingent consideration, $1.3 million of acquisition related expenses and compensation and $0.8 million of employee severance charges.

[6] Restructuring and other includes a $17.7 million fair value adjustment to increase the MiR acquisition contingent consideration, $0.8 million of employee severance charges, and $0.5 million acquisition related expenses and compensation, partially offset by a $7.4 million gain for the decrease in the fair value of the Universal Robots contingent consideration liability.

[7] Teradyne recorded pension and post retirement net actuarial gains of $3.5 million for the fourth quarter in 2018. See Note B: “Accounting Policies” for a discussion of Teradyne’s accounting policy.

[8] Restructuring and other includes $1.7 million of employee severance charges, $0.8 million of acquisition related expenses and compensation, partially offset by a $0.8 million gain for the decrease in the fair value of the Universal Robots contingent consideration liability.

[9] Restructuring and other includes a $5.0 million gain for the decrease in the fair value of the Universal Robots contingent consideration liability, partially offset by $3.9 million of employee severance charges and $0.8 million of acquisition related expenses and compensation.

[10] Restructuring and other includes a $3.5 million gain for the decrease in the fair value of the Universal Robots contingent consideration liability, partially offset by $2.5 million of acquisition related expenses and compensation and $2.4 million of employee severance charges.

[11] Incremental shares from the assumed conversion of the convertible notes was calculated using the difference between the average Teradyne stock price for the period and the conversion price of $31.70, multiplied by 14.5 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.

[12] Convertible notes hedge warrant shares were calculated using the difference between the average Teradyne stock price for the period and the warrant price of $39.78, multiplied by 14.5 million shares. The result of this calculation, representing the total intrinsic value of the warrant, was divided by the average Teradyne stock price for the period.