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Financial Instruments - Additional Information (Detail) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Financial Instruments and Fair Value [Line Items] |  |  |  |  |  |  |
Available-for-sale securities, realized loss |  |  |  |  | $ 400,000 | $ 0 | $ 0
Available-for-sale securities, realized gain |  |  |  |  | 1,700,000 | 2,400,000 | 1,000,000
Payments of contingent consideration |  |  |  |  |  |  | 388,000
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses |  |  | $ 583,076,000 |  | 601,660,000 | 583,076,000 |
Fair market value of investments with unrealized losses greater than one year |  |  | 2,300,000 |  | 900,000 | 2,300,000 |
Aggregate loss of investments with unrealized losses greater than one year |  |  |  |  | 500,000 | 100,000 |
Fair market value of investments with unrealized losses less than one year |  |  | 580,800,000 |  | 600,800,000 | 580,800,000 |
Aggregate loss of investments with unrealized losses less than one year |  |  |  |  | 3,600,000 | 800,000 |
Goodwill, carrying value |  |  | 781,058,000 |  | 996,033,000 | 781,058,000 | 770,515,000
Goodwill, impairment loss |  |  | 98,897,000 | [1],[2],[3] |  | 98,897,000 | 0
Gains (losses) on foreign currency transactions |  |  |  |  | 2,500,000 | (900,000) | (6,900,000)
Realized (losses) gains on foreign currency contracts |  |  |  |  | (3,000,000) | (200,000) | 5,900,000
Proceeds from sale of equity interest |  | $ 5,406,000 |  |  | 5,406,000 |  | $ 34,212,000
Equity And Debt Mutual Funds |  |  |  |  |  |  |
Financial Instruments and Fair Value [Line Items] |  |  |  |  |  |  |
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses |  |  | 1,234,000 |  | 2,560,000 | 1,234,000 |
Available for sale securities with out contractual maturity date |  |  |  |  | 14,000,000 |  |
Foreign Currency Forward Contracts |  |  |  |  |  |  |
Financial Instruments and Fair Value [Line Items] |  |  |  |  |  |  |
Gains (losses) on foreign currency transactions |  |  |  |  | $ 0 | (100,000) |
Fair Value, Measurements, Nonrecurring |  |  |  |  |  |  |
Financial Instruments and Fair Value [Line Items] |  |  |  |  |  |  |
Goodwill, carrying value |  |  | 372,300,000 |  |  | 372,300,000 |
Goodwill, fair value |  |  | $ 273,438,000 |  |  | 273,438,000 |
Goodwill, impairment loss |  |  |  |  |  | $ 98,897,000 |
Scenario, Forecast | Universal Robots |  |  |  |  |  |  |
Financial Instruments and Fair Value [Line Items] |  |  |  |  |  |  |
Payments of contingent consideration | $ 15,000,000 |  |  |  |  |  |
EBITDA contingent consideration amount, percentage | 100.00% |  |  |  |  |  |
Accounts Receivable | Customer 1 | Minimum |  |  |  |  |  |  |
Financial Instruments and Fair Value [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage |  |  |  |  | 10.00% |  |
Accounts Receivable | Customer 2 | Minimum |  |  |  |  |  |  |
Financial Instruments and Fair Value [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage |  |  |  |  |  | 10.00% |
[1] | Dividends declared by Teradyne's Board of Directors were paid in the second, third and fourth quarters of 2014.
[2] | In the fourth quarter ended December 31, 2014, Teradyne recorded a goodwill impairment charge of $98.9 million in its Wireless Test segment.
[3] | In the fourth quarter ended December 31, 2014, Teradyne recorded pension and post retirement net actuarial losses of $46.6 million. See Note B: "Accounting Policies" for a discussion of our accounting policy.

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