Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 29, 2019	[3]	Jun. 30, 2019	[4]	Mar. 31, 2019	[5]	Dec. 31, 2018		Sep. 30, 2018	[8]	Jul. 01, 2018	[9]	Apr. 01, 2018	[10]	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018	Mar. 31, 2017	Feb. 28, 2016
Summary Of Significant Accounting Policies [Line Items]
Standard warranty period																	12 months
Depreciation over life to cost of revenues and selling and administrative expenses, years																	6 years
Net book value of internally manufactured test systems sold																	$ 5,000	$ 3,800	$ 3,600
Cumulative effect adjustment to increase retained earnings and deferred tax assets									$ 12,679									12,679
Income tax provision (benefit)	$ 23,811	[1],[2]	$ 15,873		$ 33,780		$ (15,159)		(32,662)	[6],[7]	$ 20,863		$ 18,975		$ 8,846		58,304	16,022	266,720
Advertising costs																	16,600	15,400	9,100
Losses (gains) on foreign currency transactions																	(1,600)	(2,500)	2,900
Trade Accounts Receivable	143,600								52,200								143,600	52,200
Lease right-of-use assets	57,539																57,539			$ 50,100			$ 50,100
Operating Lease, Liability	$ 65,325																65,325			$ 54,300			$ 54,300
ASU 2016-09
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment to increase retained earnings and deferred tax assets																						$ 39,000
Income tax provision (benefit)																	$ 4,900	7,600	6,300
ASU 2017-07
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in income from operations																			$ (5,000)
Retained Earnings
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment to increase retained earnings and deferred tax assets									$ 12,679									$ 12,679
Retained Earnings | ASU 2016-01
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in adoption of new accounting guidance amount																					$ 3,100
Accumulated Other Comprehensive Income (Loss) | ASU 2016-01
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in adoption of new accounting guidance amount																					$ (3,100)

[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.