Basis of Presentation (Policies)	6 Months Ended
Apr. 04, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation: The accompanying Condensed Consolidated Financial Statements included herein have been prepared by Plexus Corp. and its subsidiaries (together “Plexus” or the “Company”) without audit and pursuant to the rules and regulations of the United States (“U.S.”) Securities and Exchange Commission (“SEC”). The accompanying Condensed Consolidated Financial Statements reflect all adjustments, which include normal recurring adjustments necessary for the fair statement of the consolidated financial position of the Company as of April 4, 2020 and September 28, 2019, the results of operations and shareholders' equity for the three and six months ended April 4, 2020 and March 30, 2019, and the cash flows for the same six month periods. The Company’s fiscal year ends on the Saturday closest to September 30. The Company uses a “4-4-5” weekly accounting system for the interim periods in each quarter. Each quarter, therefore, ends on a Saturday at the end of the 4-4-5 period. Periodically, an additional week must be added to the fiscal year to re-align with the Saturday closest to September 30. Fiscal 2020 includes 53 weeks; therefore, the first quarter of fiscal 2020 included 14 weeks while all other fiscal quarters presented herein included 13 weeks. Certain information and footnote disclosures, normally included in financial statements prepared in accordance with generally accepted accounting principles in the United States of America ("U.S. GAAP"), have been condensed or omitted pursuant to the SEC’s rules and regulations dealing with interim financial statements. However, the Company believes that the disclosures made in the Condensed Consolidated Financial Statements included herein are adequate to make the information presented not misleading. It is suggested that these Condensed Consolidated Financial Statements be read in conjunction with the Consolidated Financial Statements and notes thereto included in the Company’s 2019 Annual Report on Form 10-K.
Recently Adopted Accounting Pronouncements & Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements: In May 2014, the FASB issued ASU 2014-09, which requires an entity to recognize revenue relating to contracts with customers that depicts the transfer of promised goods or services to customers in an amount reflecting the consideration to which the entity expects to be entitled in exchange for such goods or services ("Topic 606"). On September 30, 2018, the Company adopted and applied Topic 606 to all contracts using the modified retrospective method of adoption. Upon adoption, the Company recognized an increase to its fiscal 2019 beginning Retained earnings balance of $7.8 million. In February 2016, the FASB issued ASU 2016-02 (“Topic 842”), which is intended to improve financial reporting of lease transactions by requiring lessees to recognize most leases as a right-of-use (“ROU”) asset and lease liability on their balance sheets for the rights and obligations created by leases, but record expenses on their income statements in a similar manner. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. ASU 2016-02 also requires disclosures regarding the amount, timing and judgments related to accounting for an entity’s leases and related cash flows. On September 29, 2019, the Company adopted Topic 842 using the modified retrospective method of adoption, which allows financial information for comparative periods prior to adoption not to be updated. The Company recognized right-of-use assets and operating lease liabilities on its Consolidated Balance Sheets, but the standard did not have a material impact on its Consolidated Statements of Comprehensive Income or Consolidated Statements of Cash Flows. ASC 842 provides optional practical expedients to assist with transition to the new standard. Management elected the package of practical expedients offered, which allows entities to not reassess: (i) whether any contracts prior to the adoption date are or contain leases, (ii) lease classification, and (iii) whether capitalized initial direct costs continue to meet the definition of initial direct costs under the new guidance. For all new and modified leases after adoption, management elected the short-term lease recognition exemption for all of the Company’s leases that qualify, in addition to the practical expedient to not separate lease and nonlease components. Refer to Note 7, "Leases," for further information. In August 2017, the FASB issued ASU 2017-12 related to the accounting for hedging activities. The pronouncement expands and refines hedge accounting, aligns the recognition and presentation of the effects of hedging instruments and hedge items in the financial statements, and includes certain targeted improvements to ease the application of current guidance related to the assessment of hedge effectiveness. The Company adopted this guidance during the first quarter of fiscal 2020 with no material impact to the Company's Consolidated Financial Statements; however, the impact of the new standard on future periods will depend on the facts and circumstances of future transactions. Recently Issued Accounting Pronouncements Not Yet Adopted: In June 2016, the FASB issued ASU 2016-13, which replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and required consideration of a broader range of reasonable and supportable information to inform credit loss estimates. This guidance is effective for the Company beginning in the first quarter of fiscal year 2021. Early adoption is permitted. The Company is currently in the process of assessing the impact of the adoption of the new standard on its Consolidated Financial Statements. In March 2020, the FASB issued ASU 2020-04, which provides guidance in accounting for contracts, hedging relationships, and other transactions that are affected by reference rate reform. The optional expedients and exceptions in this guidance are allowed to be applied by the Company starting with the second quarter of fiscal year 2020. The Company is currently in the process of assessing the impacts of the adoption on its Consolidated Financial Statements. The Company believes that no other recently issued accounting standards will have a material impact on its Consolidated Financial Statements, or apply to its operations.
Fair Value of Financial Instruments	Fair Value Measurements: Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (or exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The Company uses quoted market prices when available or discounted cash flows to calculate fair value. The accounting guidance establishes a fair value hierarchy based on three levels of inputs that may be used to measure fair value. The input levels are: Level 1: Quoted (observable) market prices in active markets for identical assets or liabilities. Level 2: Inputs other than Level 1 that are observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability. Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the asset or liability.

Basis of Presentation (Policies)

6 Months Ended

Apr. 04, 2020

Basis of Presentation:

The accompanying Condensed Consolidated Financial Statements included herein have been prepared by Plexus Corp. and its subsidiaries (together “Plexus” or the “Company”) without audit and pursuant to the rules and regulations of the United States (“U.S.”) Securities and Exchange Commission (“SEC”). The accompanying Condensed Consolidated Financial Statements reflect all adjustments, which include normal recurring adjustments necessary for the fair statement of the consolidated financial position of the Company as of April 4, 2020 and September 28, 2019, the results of operations and shareholders' equity for the three and six months ended April 4, 2020 and March 30, 2019, and the cash flows for the same six month periods.

The Company’s fiscal year ends on the Saturday closest to September 30. The Company uses a “4-4-5” weekly accounting system for the interim periods in each quarter. Each quarter, therefore, ends on a Saturday at the end of the 4-4-5 period. Periodically, an additional week must be added to the fiscal year to re-align with the Saturday closest to September 30. Fiscal 2020 includes 53 weeks; therefore, the first quarter of fiscal 2020 included 14 weeks while all other fiscal quarters presented herein included 13 weeks.

Certain information and footnote disclosures, normally included in financial statements prepared in accordance with generally accepted accounting principles in the United States of America ("U.S. GAAP"), have been condensed or omitted pursuant to the SEC’s rules and regulations dealing with interim financial statements. However, the Company believes that the disclosures made in the Condensed Consolidated Financial Statements included herein are adequate to make the information presented not misleading. It is suggested that these Condensed Consolidated Financial Statements be read in conjunction with the Consolidated Financial Statements and notes thereto included in the Company’s 2019 Annual Report on Form 10-K.

Recently Adopted Accounting Pronouncements & Recently Issued Accounting Pronouncements Not Yet Adopted

Recently Adopted Accounting Pronouncements:

In May 2014, the FASB issued ASU 2014-09, which requires an entity to recognize revenue relating to contracts with customers that depicts the transfer of promised goods or services to customers in an amount reflecting the consideration to which the entity expects to be entitled in exchange for such goods or services ("Topic 606"). On September 30, 2018, the Company adopted and applied Topic 606 to all contracts using the modified retrospective method of adoption. Upon adoption, the Company recognized an increase to its fiscal 2019 beginning Retained earnings balance of $7.8 million.

In February 2016, the FASB issued ASU 2016-02 (“Topic 842”), which is intended to improve financial reporting of lease transactions by requiring lessees to recognize most leases as a right-of-use (“ROU”) asset and lease liability on their balance sheets for the rights and obligations created by leases, but record expenses on their income statements in a similar manner. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. ASU 2016-02 also requires disclosures regarding the amount, timing and judgments related to accounting for an entity’s leases and related cash flows.

On September 29, 2019, the Company adopted Topic 842 using the modified retrospective method of adoption, which allows financial information for comparative periods prior to adoption not to be updated. The Company recognized right-of-use assets and operating lease liabilities on its Consolidated Balance Sheets, but the standard did not have a material impact on its Consolidated Statements of Comprehensive Income or Consolidated Statements of Cash Flows.

ASC 842 provides optional practical expedients to assist with transition to the new standard. Management elected the package of practical expedients offered, which allows entities to not reassess: (i) whether any contracts prior to the adoption date are or contain leases, (ii) lease classification, and (iii) whether capitalized initial direct costs continue to meet the definition of initial

direct costs under the new guidance. For all new and modified leases after adoption, management elected the short-term lease recognition exemption for all of the Company’s leases that qualify, in addition to the practical expedient to not separate lease and nonlease components. Refer to Note 7, "Leases," for further information.

In August 2017, the FASB issued ASU 2017-12 related to the accounting for hedging activities. The pronouncement expands and refines hedge accounting, aligns the recognition and presentation of the effects of hedging instruments and hedge items in the financial statements, and includes certain targeted improvements to ease the application of current guidance related to the assessment of hedge effectiveness. The Company adopted this guidance during the first quarter of fiscal 2020 with no material impact to the Company's Consolidated Financial Statements; however, the impact of the new standard on future periods will depend on the facts and circumstances of future transactions.

Recently Issued Accounting Pronouncements Not Yet Adopted:

In June 2016, the FASB issued ASU 2016-13, which replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and required consideration of a broader range of reasonable and supportable information to inform credit loss estimates. This guidance is effective for the Company beginning in the first quarter of fiscal year 2021. Early adoption is permitted. The Company is currently in the process of assessing the impact of the adoption of the new standard on its Consolidated Financial Statements.

In March 2020, the FASB issued ASU 2020-04, which provides guidance in accounting for contracts, hedging relationships, and other transactions that are affected by reference rate reform. The optional expedients and exceptions in this guidance are allowed to be applied by the Company starting with the second quarter of fiscal year 2020. The Company is currently in the process of assessing the impacts of the adoption on its Consolidated Financial Statements.

The Company believes that no other recently issued accounting standards will have a material impact on its Consolidated Financial Statements, or apply to its operations.

Fair Value of Financial Instruments

Fair Value Measurements:

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (or exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The Company uses quoted market prices when available or discounted cash flows to calculate fair value. The accounting guidance establishes a fair value hierarchy based on three levels of inputs that may be used to measure fair value. The input levels are:

Level 1: Quoted (observable) market prices in active markets for identical assets or liabilities.

Level 2: Inputs other than Level 1 that are observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability.

Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the asset or liability.