BASIS OF PRESENTATION (Policies)	3 Months Ended
Mar. 28, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Use of Estimates	The preparation of unaudited condensed consolidated financial statements in accordance with U.S. GAAP requires that the Company make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosure of contingent assets and liabilities. On an on-going basis, the Company evaluates its estimates, judgments, and methodologies. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates under different assumptions or conditions. Changes in estimates are reflected in reported results in the period in which they become known. On March 11, 2020, the World Health Organization declared the outbreak of a strain of novel coronavirus disease, COVID-19, a global pandemic. The COVID-19 pandemic is dynamic and expanding, and its ultimate scope, duration and effects are uncertain. This pandemic has and continues to result in, and any future epidemic or pandemic crises may potentially result in, direct and indirect adverse effects on the Company’s industry and customers, which in turn has (with respect to COVID-19) and may (with respect to future epidemics or crises) impact the Company’s business, results of operations and financial condition. Further, the COVID-19 pandemic may also affect the Company’s operating and financial results in a manner that is not presently known to the Company or that the Company currently does not expect to present significant risks to its operations or financial results. As of the date of issuance of these unaudited condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update estimates, judgments or revise the carrying value of any assets or liabilities. These estimates may change, as new events occur and additional information is obtained, and are recognized in the condensed consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s condensed consolidated financial statements.
Consolidation	The Company’s unaudited condensed consolidated financial statements reflect its financial statements and those of its subsidiaries in which the Company holds a controlling financial interest. For consolidated entities in which the Company owns or is exposed to less than 100% of the economics, the Company records net income (loss) attributable to noncontrolling interests in its consolidated statements of income equal to the percentage of the economic or ownership interest retained in such entities by the respective noncontrolling parties. Intercompany balances and transactions are eliminated in consolidation.
Fiscal Period	The Company’s fiscal year is typically based on 52-weeks, with each quarter composed of 13 weeks ending on the last Saturday on, or closest to, March 31, June 30, September 30, and December 31.
Segment Reporting	The Company reports its results in three reportable segments: Research Models and Services (RMS), Discovery and Safety Assessment (DSA), and Manufacturing Support (Manufacturing). The Company’s RMS reportable segment includes the Research Models, Research Model Services, and Research Products businesses. Research Models includes the commercial production and sale of small research models, as well as the supply of large research models. Research Model Services includes: Genetically Engineered Models and Services (GEMS), which performs contract breeding and other services associated with genetically engineered models; Research Animal Diagnostic Services (RADS), which provides health monitoring and diagnostics services related to research models; and Insourcing Solutions (IS), which provides colony management of its clients’ research operations (including recruitment, training, staffing, and management services). Research Products supplies controlled, consistent, customized primary cells and blood components derived from normal and mobilized peripheral blood, bone marrow, and cord blood. The Company’s DSA reportable segment includes services required to take a drug through the early development process including discovery services, which are non-regulated services to assist clients with the identification, screening, and selection of a lead compound for drug development, and regulated and non-regulated (GLP and non-GLP) safety assessment services. The Company’s Manufacturing reportable segment includes Microbial Solutions, which provides in vitro (non-animal) lot-release testing products, microbial detection products, and species identification services; Biologics Testing Services (Biologics), which performs specialized testing of biologics; and Avian Vaccine Services (Avian), which supplies specific-pathogen-free chicken eggs and chickens.
Newly Adopted and Newly Issued Accounting Pronouncements	In August 2018, the Financial Accounting Standards Board (FASB) issued ASU 2018-15, “Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computer Arrangement that is a Service Contract.” ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820) - Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement.” ASU 2018-13 removes the disclosure requirement for the amount and reasons for transfers between Level 1 and Level 2 fair value measurements as well as the process for Level 3 fair value measurements. In addition, the ASU adds the disclosure requirements for changes in unrealized gains and losses included in Other comprehensive income (loss) for recurring Level 3 fair value measurements held at the end of the reporting period as well as the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-14, “Compensation Retirement Benefits - Defined Benefit Plans -General (Subtopic 715-20).” ASU 2018-14 removes the requirements to disclose the amounts in Accumulated other comprehensive income (loss) expected to be recognized as components of net periodic benefit cost over the next fiscal year and the related party disclosures about the amount of future annual benefits covered by insurance contracts. In addition, the ASU adds the requirement to disclose an explanation for any significant gains and losses related to changes in the benefit obligation for the period. This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU 2017-04, “Simplifying the Test for Goodwill Impairment.” The standard simplifies the accounting for goodwill impairment by removing Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. This standard became effective for the Company in the three months ended March 28, 2020 and did not have an impact on the unaudited condensed consolidated financial statements and related disclosures. The Company performs its annual impairment test during the fourth quarter of a fiscal year and does not expect any significant impact on the consolidated financial statements and related disclosures. In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses”. The standard, including subsequently issued amendments, requires a financial asset measured at amortized cost basis, such as trade and notes receivables, to be presented at the net amount expected to be collected based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures. Newly Issued Accounting Pronouncements In March 2020, the FASB issued ASU 2020-04, “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting.” The ASU offers temporary optional expedients and exceptions for applying U.S. GAAP to modifications to agreements such as loans, debt securities, derivatives, and borrowings which reference LIBOR or another reference rate that is expected to be discontinued by December 31, 2021. The expedients and exceptions provided by the standard do not apply to modifications made and hedging relationships entered into or evaluated after December 31, 2022, except for hedging relationships existing as of December 31, 2022 that an entity has elected certain optional expedients for and are retained through the end of the hedging relationship. The ASU is effective until December 31, 2022 when the replacement for LIBOR is expected to be completed. The interest rate on the Company’s senior credit facility, which matures in fiscal year 2023, is linked to LIBOR. The Company is in the process of evaluating options for transitioning away from the senior credit facility’s use of LIBOR and expects to be completed by the time LIBOR is phased out. The Company is still evaluating the impact this standard will have on its consolidated financial statements and related disclosures and has yet to elect an adoption date. In January 2020, the FASB issued ASU 2020-01, “Investments-Equity Securities (Topic 321), Investments-Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815).” ASU 2020-01 states any equity security transitioning from the alternative method of accounting under Topic 321 to the equity method, or vice versa, due to an observable transaction will be remeasured immediately before the transition. In addition, the ASU clarifies the accounting for certain non-derivative forward contracts or purchased call options to acquire equity securities stating such instruments will be measured using the fair value principles of Topic 321 before settlement or exercise. The ASU is effective for fiscal years beginning after December 15, 2020, and will be applied on a prospective basis. Early adoption is permitted. The Company is still evaluating the impact this standard will have on its consolidated financial statements and related disclosures, but does not believe there will be a material impact upon adoption. In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes.” ASU 2019-12 simplifies the accounting for income taxes by removing exceptions within the general principles of Topic 740 regarding the calculation of deferred tax liabilities, the incremental approach for intraperiod tax allocation, and calculating income taxes in an interim period. In addition, the ASU adds clarifications to the accounting for franchise tax (or similar tax), which is partially based on income, evaluating tax basis of goodwill recognized from a business combination, and reflecting the effect of any enacted changes in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. The ASU is effective for fiscal years beginning after December 15, 2020, and will be applied either retrospectively or prospectively based upon the applicable amendments. Early adoption is permitted. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures.

BASIS OF PRESENTATION (Policies)

3 Months Ended

Mar. 28, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The preparation of unaudited condensed consolidated financial statements in accordance with U.S. GAAP requires that the Company make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosure of contingent assets and liabilities. On an on-going basis, the Company evaluates its estimates, judgments, and methodologies. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates under different assumptions or conditions. Changes in estimates are reflected in reported results in the period in which they become known.

On March 11, 2020, the World Health Organization declared the outbreak of a strain of novel coronavirus disease, COVID-19, a global pandemic. The COVID-19 pandemic is dynamic and expanding, and its ultimate scope, duration and effects are uncertain. This pandemic has and continues to result in, and any future epidemic or pandemic crises may potentially result in, direct and indirect adverse effects on the Company’s industry and customers, which in turn has (with respect to COVID-19) and may (with respect to future epidemics or crises) impact the Company’s business, results of operations and financial condition. Further, the COVID-19 pandemic may also affect the Company’s operating and financial results in a manner that is not presently known to the Company or that the Company currently does not expect to present significant risks to its operations or financial results. As of the date of issuance of these unaudited condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update estimates, judgments or revise the carrying value of any assets or liabilities. These estimates may change, as new events occur and additional information is obtained, and are recognized in the condensed consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s condensed consolidated financial statements.

Consolidation

The Company’s unaudited condensed consolidated financial statements reflect its financial statements and those of its subsidiaries in which the Company holds a controlling financial interest. For consolidated entities in which the Company owns or is exposed to less than 100% of the economics, the Company records net income (loss) attributable to noncontrolling interests in its consolidated statements of income equal to the percentage of the economic or ownership interest retained in such entities by the respective noncontrolling parties. Intercompany balances and transactions are eliminated in consolidation.

Fiscal Period

The Company’s fiscal year is typically based on 52-weeks, with each quarter composed of 13 weeks ending on the last Saturday on, or closest to, March 31, June 30, September 30, and December 31.

Segment Reporting

The Company reports its results in three reportable segments: Research Models and Services (RMS), Discovery and Safety Assessment (DSA), and Manufacturing Support (Manufacturing). The Company’s RMS reportable segment includes the Research Models, Research Model Services, and Research Products businesses. Research Models includes the commercial production and sale of small research models, as well as the supply of large research models. Research Model Services includes: Genetically Engineered Models and Services (GEMS), which performs contract breeding and other services associated with genetically engineered models; Research Animal Diagnostic Services (RADS), which provides health monitoring and diagnostics services related to research models; and Insourcing Solutions (IS), which provides colony management of its clients’ research operations (including recruitment, training, staffing, and management services). Research Products supplies controlled, consistent, customized primary cells and blood components derived from normal and mobilized peripheral blood, bone marrow, and cord blood. The Company’s DSA reportable segment includes services required to take a drug through the early development process including discovery services, which are non-regulated services to assist clients with the identification, screening, and selection of a lead compound for drug development, and regulated and non-regulated (GLP and non-GLP) safety assessment services. The Company’s Manufacturing reportable segment includes Microbial Solutions, which provides in vitro (non-animal) lot-release testing products, microbial detection products, and species identification services; Biologics Testing Services (Biologics), which performs specialized testing of biologics; and Avian Vaccine Services (Avian), which supplies specific-pathogen-free chicken eggs and chickens.

Newly Adopted and Newly Issued Accounting Pronouncements

In August 2018, the Financial Accounting Standards Board (FASB) issued ASU 2018-15, “Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computer Arrangement that is a Service Contract.” ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures.

In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820) - Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement.” ASU 2018-13 removes the disclosure requirement for the amount and reasons for transfers between Level 1 and Level 2 fair value measurements as well as the process for Level 3 fair value measurements. In addition, the ASU adds the disclosure requirements for changes in unrealized gains and losses included in Other comprehensive income (loss) for recurring Level 3 fair value measurements held at the end of the reporting period as well as the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures.

In August 2018, the FASB issued ASU 2018-14, “Compensation Retirement Benefits - Defined Benefit Plans -General (Subtopic 715-20).” ASU 2018-14 removes the requirements to disclose the amounts in Accumulated other comprehensive income (loss) expected to be recognized as components of net periodic benefit cost over the next fiscal year and the related party disclosures about the amount of future annual benefits covered by insurance contracts. In addition, the ASU adds the requirement to disclose an explanation for any significant gains and losses related to changes in the benefit obligation for the period. This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures.

In January 2017, the FASB issued ASU 2017-04, “Simplifying the Test for Goodwill Impairment.” The standard simplifies the accounting for goodwill impairment by removing Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. This standard became effective for the Company in the three months ended March 28, 2020 and did not have an impact on the unaudited condensed consolidated financial statements and related disclosures. The Company performs its annual impairment test during the fourth quarter of a fiscal year and does not expect any significant impact on the consolidated financial statements and related disclosures.

In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses”. The standard, including subsequently issued amendments, requires a financial asset measured at amortized cost basis, such as trade and notes receivables, to be presented at the net amount expected to be collected based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. This standard became effective for the Company in the three months ended March 28, 2020 and did not have a significant impact on the unaudited condensed consolidated financial statements and related disclosures.

Newly Issued Accounting Pronouncements

In March 2020, the FASB issued ASU 2020-04, “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting.” The ASU offers temporary optional expedients and exceptions for applying U.S. GAAP to modifications to agreements such as loans, debt securities, derivatives, and borrowings which reference LIBOR or another reference rate that is expected to be discontinued by December 31, 2021. The expedients and exceptions provided by the standard do not apply to modifications made and hedging relationships entered into or evaluated after December 31, 2022, except for hedging relationships existing as of December 31, 2022 that an entity has elected certain optional expedients for and are retained through the end of the hedging relationship. The ASU is effective until December 31, 2022 when the replacement for LIBOR is expected to be completed. The interest rate on the Company’s senior credit facility, which matures in fiscal year 2023, is linked to LIBOR. The Company is in the process of evaluating options for transitioning away from the senior credit facility’s use of LIBOR and expects to be completed by the time LIBOR is phased out. The Company is still evaluating the impact this standard will have on its consolidated financial statements and related disclosures and has yet to elect an adoption date.

In January 2020, the FASB issued ASU 2020-01, “Investments-Equity Securities (Topic 321), Investments-Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815).” ASU 2020-01 states any equity security transitioning

from the alternative method of accounting under Topic 321 to the equity method, or vice versa, due to an observable transaction will be remeasured immediately before the transition. In addition, the ASU clarifies the accounting for certain non-derivative forward contracts or purchased call options to acquire equity securities stating such instruments will be measured using the fair value principles of Topic 321 before settlement or exercise. The ASU is effective for fiscal years beginning after December 15, 2020, and will be applied on a prospective basis. Early adoption is permitted. The Company is still evaluating the impact this standard will have on its consolidated financial statements and related disclosures, but does not believe there will be a material impact upon adoption.

In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes.” ASU 2019-12 simplifies the accounting for income taxes by removing exceptions within the general principles of Topic 740 regarding the calculation of deferred tax liabilities, the incremental approach for intraperiod tax allocation, and calculating income taxes in an interim period. In addition, the ASU adds clarifications to the accounting for franchise tax (or similar tax), which is partially based on income, evaluating tax basis of goodwill recognized from a business combination, and reflecting the effect of any enacted changes in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. The ASU is effective for fiscal years beginning after December 15, 2020, and will be applied either retrospectively or prospectively based upon the applicable amendments. Early adoption is permitted. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures.