Basis of Presentation	6 Months Ended
Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	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 March 31, 2018 and September 30, 2017, and the results of operations for the three and six months ended March 31, 2018 and April 1, 2017, 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. All 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 2017 Annual Report on Form 10-K. Certain prior period amounts have been reclassified to conform to the current period presentation. Recently Issued Accounting Pronouncements Not Yet Adopted: In August 2017, the Financial Accounting Standards Board (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. This guidance is effective for the Company beginning in the first quarter of fiscal year 2020 and early adoption is permitted. The Company is finalizing its assessment of the impact of the guidance, but does not believe it will have a material impact on the Company's Condensed Consolidated Financial Statements. In October 2016, the FASB issued ASU 2016-16 related to the income tax consequences of intra-entity transfers of assets other than inventory. The new standard eliminates the exception for an intra-entity transfer of an asset other than inventory and requires an entity to recognize the income tax consequences when the transfer occurs. This guidance is effective for the Company beginning in the first quarter of fiscal year 2019 and early adoption is permitted. This guidance should be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. The Company is currently assessing the impact this new standard may have on its Condensed Consolidated Financial Statements. In August 2016, the FASB issued ASU 2016-15 related to the classification of certain cash receipts and cash payments, which clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flows. The new standard addresses certain issues where diversity in practice was identified. It also amends existing guidance, which is principles based and often requires judgment to determine the appropriate classification of cash flows as operating, investing or financing activities and clarifies how the predominance principle should be applied when cash receipts and cash payments have aspects of more than one class of cash flows. This guidance is effective for the Company beginning in the first quarter of fiscal year 2019. Early adoption is permitted. The Company is currently assessing the impact this new standard may have on its Condensed Consolidated Statements of Cash Flows. In February 2016, the FASB issued ASU 2016-02, which requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. This guidance is effective for the Company beginning in the first quarter of fiscal year 2020. Early adoption is permitted. The Company is currently in the process of assessing the impact of the adoption of the new standard on its Condensed Consolidated Financial Statements and the timing of adoption. 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"). Topic 606 also requires disclosures enabling users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers and is effective for the Company beginning in the first quarter of fiscal year 2019. The Company developed a comprehensive project plan that includes a global cross-functional team of representatives to conduct an assessment of Topic 606 and its potential impacts on the Company. The project plan includes analyzing the standard’s impact on the Company’s various revenue streams, comparing its historical accounting policies and practices to the requirements of the new standard, and identifying potential differences from applying the requirements of the new standard to its contracts. The Company is in the process of identifying and implementing appropriate changes to its current accounting policies, business processes, systems and controls to support revenue recognition and disclosures under Topic 606. The Company has determined that the new standard will result in a change to the timing of revenue recognition for a significant portion of the Company's revenue, whereby revenue will be recognized "over time," as products are produced, as opposed to at a "point in time" upon physical delivery. The new standard is expected to have a material impact on the Company's consolidated financial statements upon initial adoption, primarily as the Company recognizes an increase in contract assets for unbilled receivables with a corresponding reduction in finished goods and work-in-process inventory. The Company expects to adopt Topic 606 at the beginning of fiscal year 2019 using the modified retrospective approach. 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.

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 March 31, 2018 and September 30, 2017, and the results of operations for the three and six months ended March 31, 2018 and April 1, 2017, 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. All 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 2017 Annual Report on Form 10-K.

Certain prior period amounts have been reclassified to conform to the current period presentation.

Recently Issued Accounting Pronouncements Not Yet Adopted:

In August 2017, the Financial Accounting Standards Board (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. This guidance is effective for the Company beginning in the first quarter of fiscal year 2020 and early adoption is permitted. The Company is finalizing its assessment of the impact of the guidance, but does not believe it will have a material impact on the Company's Condensed Consolidated Financial Statements.

In October 2016, the FASB issued ASU 2016-16 related to the income tax consequences of intra-entity transfers of assets other than inventory. The new standard eliminates the exception for an intra-entity transfer of an asset other than inventory and requires an entity to recognize the income tax consequences when the transfer occurs. This guidance is effective for the Company beginning in the first quarter of fiscal year 2019 and early adoption is permitted. This guidance should be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. The Company is currently assessing the impact this new standard may have on its Condensed Consolidated Financial Statements.

In August 2016, the FASB issued ASU 2016-15 related to the classification of certain cash receipts and cash payments, which clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flows. The new standard addresses certain issues where diversity in practice was identified. It also amends existing guidance, which is principles based and often requires judgment to determine the appropriate classification of cash flows as operating, investing or financing activities and clarifies how the predominance principle should be applied when cash receipts and cash payments have aspects of more than one class of cash flows. This guidance is effective for the Company beginning in the first quarter of fiscal year 2019. Early adoption is permitted. The Company is currently assessing the impact this new standard may have on its Condensed Consolidated Statements of Cash Flows.

In February 2016, the FASB issued ASU 2016-02, which requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. This guidance is effective for the Company beginning in the first quarter of fiscal year 2020. Early adoption is permitted. The Company is currently in the process of assessing the impact of the adoption of the new standard on its Condensed Consolidated Financial Statements and the timing of adoption.

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"). Topic 606 also requires disclosures enabling users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers and is effective for the Company beginning in the first quarter of fiscal year 2019.

The Company developed a comprehensive project plan that includes a global cross-functional team of representatives to conduct an assessment of Topic 606 and its potential impacts on the Company. The project plan includes analyzing the standard’s impact on the Company’s various revenue streams, comparing its historical accounting policies and practices to the requirements of the new standard, and identifying potential differences from applying the requirements of the new standard to its contracts. The Company is in the process of identifying and implementing appropriate changes to its current accounting policies, business processes, systems and controls to support revenue recognition and disclosures under Topic 606.

The Company has determined that the new standard will result in a change to the timing of revenue recognition for a significant portion of the Company's revenue, whereby revenue will be recognized "over time," as products are produced, as opposed to at a "point in time" upon physical delivery. The new standard is expected to have a material impact on the Company's consolidated financial statements upon initial adoption, primarily as the Company recognizes an increase in contract assets for unbilled receivables with a corresponding reduction in finished goods and work-in-process inventory. The Company expects to adopt Topic 606 at the beginning of fiscal year 2019 using the modified retrospective approach.

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.