Borrowing Facilities (Details) ฿ in Millions, $ in Millions		6 Months Ended	12 Months Ended
	Jul. 20, 2018 USD ($)	Jun. 30, 2018 THB (฿)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 12, 2015 USD ($)
Line of Credit Facility [Line Items]
Derivative Notional Amount						$ 148.8	$ 155.3
Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit Agreement description		As of June 30, 2018, the Company had a $430 million Credit Agreement (the Credit Agreement) with JPMorgan Chase Bank, N.A. as administrative agent and collateral agent (the Administrative Agent), and the financial institutions acting as lenders thereunder from time to time. This Credit Agreement provided for a five-year $200 million revolving credit facility (the Revolving Credit Facility) and a five-year $230 million term loan facility (the Term Loan). The Revolving Credit Facility was available for general corporate purposes, could be drawn in foreign currencies up to an amount equivalent to $20 million, and could be used for letters of credit up to $20 million. The Credit Agreement included an accordion feature, pursuant to which total commitments under the facility could be increased by an additional $150 million, subject to satisfaction of certain conditions.
Credit Agreement capacity						430.0
Description of variable interest rate basis		Interest on outstanding borrowings under the Credit Agreement accrued, at our option, at (a) the adjusted London interbank offered rate (LIBOR) plus 1.25% to 2.25%, or (b) the alternative base rate plus 0.25% to 1.25%, and was payable quarterly in arrears. The alternative base rate was equal to the highest of (i) the Administrative Agent’s prime rate, (ii) the federal funds rate plus 0.50% and (iii) the adjusted LIBOR rate plus 1.00%. The margin on the interest rates fluctuated based upon the ratio of the Company’s debt to its consolidated EBITDA.
Credit Agreement covenant terms		The Credit Agreement was generally secured by a pledge of (a) all the capital stock of the Company’s domestic subsidiaries and 65% of the capital stock of its directly owned foreign subsidiaries, (b) any debt owed to Benchmark and its subsidiaries and (c) all or substantially all other personal property of Benchmark and its domestic subsidiaries (including, accounts receivable, contract assets, inventory and fixed assets of Benchmark and its domestic subsidiaries), in each case, subject to customary exceptions and limitations. The Credit Agreement contained financial covenants as to debt leverage and interest coverage, and certain customary affirmative and negative covenants, including restrictions on our ability to incur additional debt and liens, pay dividends, repurchase shares, sell assets and merge or consolidate with other persons. Amounts due under the Credit Agreement could be accelerated upon specified events of default, including a failure to pay amounts due, breach of a covenant, material inaccuracy of a representation, or occurrence of bankruptcy or insolvency, subject, in some cases, to cure periods.
Credit agreement, secured by percentage of stock of the Company's domestic subsidiaries		100.00%
Credit agreement, secured by percentage of voting capital stock of each direct foreign subsidiary		65.00%
Credit Agreement covenant compliance		As of June 30, 2018 and December 31, 2017, the Company was in compliance with all of these covenants and restrictions.
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement capacity						200.0
Term period		5 years
Possible increase to total commitments under Credit Agreement						150.0
Letters of credit outstanding amount						2.8
Revolving credit facility, available for future borrowings						197.2
Term Loan Facility [Member]
Line of Credit Facility [Line Items]
Term period		5 years
Term Loan proceeds								$ 230.0
Term Loan frequency of periodic payments		quarterly
Derivative Notional Amount						148.8
Principal amount						198.4
Term Loan Facility [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative Notional Amount						148.8
Term Loan Facility [Member] | Scenario Forecast [Member]
Line of Credit Facility [Line Items]
Quarterly principal installments			$ 8.6	$ 5.8	$ 4.3
Standby Letters Of Credit [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, available for future borrowings						20.0
Foreign currencies [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, available for future borrowings						20.0
New Credit Agreement [Member] | Bank Of America Credit Agreement [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Credit Agreement capacity	$ 650.0
Possible increase to total commitments under Credit Agreement	$ 275.0
New Credit Agreement [Member] | Scenario Forecast [Member] | Bank Of America Credit Agreement [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Credit Agreement description	On July 20, 2018, the Company entered into a $650 million credit agreement (the New Credit Agreement) by and among the Company, certain of its subsidiaries, the lenders party thereto and Bank of America, N.A., as Administrative Agent, Swingline Lender and a L/C Issuer. The New Credit Agreement replaced the Credit Agreement. The New Credit Agreement is comprised of a five-year $500 million revolving credit facility (the New Revolving Credit Facility) and a five-year $150 million term loan facility (the New Term Loan Facility), both with a maturity date of July 20, 2023. A portion of the New Term Loan Facility proceeds were used to (i) refinance all indebtedness and terminate all commitments under the Credit Agreement discussed above and (ii) pay the fees, costs and expenses associated with the foregoing and the negotiation, execution and delivery of the New Credit Agreement. The New Revolving Credit Facility is available for general corporate purposes. The New Credit Agreement includes an accordion feature pursuant to which the Company is permitted to add one or more incremental term loan and/or increase commitments under the New Revolving Credit Facility in an aggregate amount not exceeding $275 million, subject to the satisfaction of certain conditions.
Credit Agreement covenant terms	The New Credit Agreement contains certain financial covenants as to interest coverage and debt leverage, and certain customary affirmative and negative covenants, including restrictions on our ability to incur additional debt and liens, pay dividends, repurchase shares, sell assets and merge or consolidate with other persons.
New Revolving Credit Facility [Member] | Bank Of America Credit Agreement [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Credit Agreement capacity	$ 500.0
Term period	5 years
Credit Agreement maturity date	Jul. 20, 2023
New Term Loan Facility [Member] | Bank Of America Credit Agreement [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Credit Agreement capacity	$ 150.0
Term period	5 years
Credit Agreement maturity date	Jul. 20, 2023
Thailand Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement maturity date		Oct. 31, 2018
Benchmark Electronics (Thailand) Public Company Limited [Member] | Thailand Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement capacity		฿ 350				$ 10.6
Minimum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee		0.30%
Maximum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee		0.40%
LIBOR Plus [Member] | Minimum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.25%
LIBOR Plus [Member] | Maximum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		2.25%
Alternate Base Rate Plus [Member] | Minimum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.25%
Alternate Base Rate Plus [Member] | Maximum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.25%