SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	The interim unaudited consolidated financial statements reflect all adjustments which in the opinion of management are necessary for a fair statement of results of operations, comprehensive income, financial condition, cash flows and stockholders' equity for the periods presented. Except as otherwise disclosed, all such adjustments are of a normal recurring nature. Operating results for the interim periods are not necessarily indicative of the results that may be expected for the full year. These interim unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements included in the Company’s 2019 Annual Report on Form 10-K. The year-end balance sheet data was derived from the audited consolidated financial statements as of December 31, 2019, but does not include all the disclosures required by accounting principles generally accepted in the United States (“GAAP”).
Use Of Estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Earnings Per Share	The Company's unvested restricted stock units that contain non-forfeitable rights to dividends are participating securities and, therefore, are included in the earnings allocation in computing earnings per share using the two-class method. Basic earnings per common share is calculated by dividing net income, adjusted for earnings allocated to participating securities, by the weighted average number of common shares outstanding. Diluted earnings per common share is calculated by dividing net income, adjusted for earnings allocated to participating securities, by the weighted average number of common shares outstanding after giving effect to all potentially dilutive common shares outstanding during the period. Potentially dilutive common shares include the dilutive effect of outstanding stock options and performance share units granted under the Company's Amended and Restated Employee Long-Term Incentive Plan and its Amended and Restated Non-Employee Director Long-Term Incentive Plan. Earnings allocable to participating securities include the portion of dividends declared as well as the portion of undistributed earnings during the period allocable to participating securities.
New Accounting Pronouncements	Adoption of New Accounting Standards On January 1, 2020, the Company adopted a new accounting standard issued by the Financial Accounting Standards Board ("FASB") which aligns the requirements for deferring implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The adoption of this standard, which the Company elected to do on a prospective basis, did not have a material impact on the Company's consolidated results of operations, financial position or cash flows. On January 1, 2020, the Company adopted a new accounting standard issued by the FASB that changes the impairment model for most financial instruments, including trade receivables, from an incurred loss method to a new forward-looking approach, based on expected losses. The estimate of expected credit losses requires entities to incorporate considerations of historical information, current information and reasonable and supportable forecasts. The adoption of this new standard, which was done using a modified retrospective transition approach, did not have a material impact on the Company's consolidated results of operations, financial position or cash flows. See Note 15 for further details on the Company's allowance for credit losses policy. New Accounting Standards to be Adopted In March 2020, the FASB issued a new accounting standard which provides temporary optional guidance to ease the potential burden in accounting for reference rate reform due to the risk of cessation of the London Interbank Offered Rate ("LIBOR"). The amendments apply only to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. The pronouncement is effective immediately and can be applied through December 31, 2022. The adoption of this standard is not expected to have a material impact on the Company’s consolidated results of operations, financial position or cash flows.
Derivative Financial Instruments	The Company uses derivative financial instruments to manage its exposure to market risks for changes in interest rates and, from time to time, foreign currencies. This strategy includes the use of interest rate swap agreements, forward-starting interest rate swap agreements, treasury lock agreements and foreign currency forward contracts to manage its exposure to movements in interest and currency rates. The Company has established policies and procedures for risk assessment and the approval, reporting and monitoring of derivative financial instrument activities. These policies prohibit holding or issuing derivative financial instruments for speculative purposes. The Company does not enter into derivative financial instruments that contain credit-risk-related contingent features or requirements to post collateral. Interest Rate Risk The Company is exposed to interest rate risk on its cash and cash equivalents and its debt obligations. Interest income earned on cash and cash equivalents may fluctuate as interest rates change; however, due to their relatively short maturities, the Company does not hedge these assets or their investment cash flows and the impact of interest rate risk is not material. The Company's debt obligations consist of fixed-rate and variable-rate debt instruments. The Company's primary objective is to achieve the lowest overall cost of funding while managing the variability in cash outflows within an acceptable range. In order to achieve this objective, the Company enters into interest rate swaps. Interest rate swaps involve the periodic exchange of payments without the exchange of underlying principal or notional amounts. Net settlements between the counterparties are recognized as an adjustment to interest expense.
Allowance for Credit Losses Policy	Allowance for Credit Losses Policy When estimating its allowance for credit losses, the Company pools its trade receivables based on the following customer types: healthcare insurers, government payers, client payers and patients. For the healthcare insurers and government payers, collection of the Company’s net revenues is normally a function of providing the complete and correct billing information within the various filing deadlines, and provided that the Company has billed the payers accurately with complete information prior to the established filing deadline, there has historically been little to no collection risk. Client payers primarily include physicians, hospitals, IDNs, ACOs, employers, other commercial laboratories and institutions for which services are performed on a wholesale basis and are billed based on negotiated fee schedules. Credit risk and ability to pay are more of a consideration for these payers. With respect to patients, implicit price concessions, which represent differences between amounts billed and the estimated consideration the Company expects to receive from patients, are recognized as a reduction of revenue. Estimates of implicit price concessions consider historical collection experience (including the period the receivables have been outstanding) and other factors including current market conditions. The Company principally estimates the allowance for credit losses by pool based on historical collection experience, the current credit worthiness of the customers, current economic conditions, expectations of future economic conditions and the period that the receivables have been outstanding. To the extent that any individual payers are identified that have deteriorated in credit quality, the Company removes the customers from their respective pools and establishes allowances based on the individual risk characteristics of such customers. Although the Company believes that its estimates for contractual allowances and patient price concessions as well as its allowance for credit losses are appropriate, it is possible that the Company will experience an impact on cash collections as a result of the impact of the COVID-19 pandemic.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

9 Months Ended

Sep. 30, 2020

The interim unaudited consolidated financial statements reflect all adjustments which in the opinion of management are necessary for a fair statement of results of operations, comprehensive income, financial condition, cash flows and stockholders' equity for the periods presented. Except as otherwise disclosed, all such adjustments are of a normal recurring nature. Operating results for the interim periods are not necessarily indicative of the results that may be expected for the full year. These interim unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements included in the Company’s 2019 Annual Report on Form 10-K. The year-end balance sheet data was derived from the audited consolidated financial statements as of December 31, 2019, but does not include all the disclosures required by accounting principles generally accepted in the United States (“GAAP”).

Use Of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Earnings Per Share

The Company's unvested restricted stock units that contain non-forfeitable rights to dividends are participating securities and, therefore, are included in the earnings allocation in computing earnings per share using the two-class method. Basic earnings per common share is calculated by dividing net income, adjusted for earnings allocated to participating securities, by the weighted average number of common shares outstanding. Diluted earnings per common share is calculated by dividing net income, adjusted for earnings allocated to participating securities, by the weighted average number of common shares outstanding after giving effect to all potentially dilutive common shares outstanding during the period. Potentially dilutive common shares include the dilutive effect of outstanding stock options and performance share units granted under the Company's Amended and Restated Employee Long-Term Incentive Plan and its Amended and Restated Non-Employee Director Long-Term Incentive Plan. Earnings allocable to participating securities include the portion of dividends declared as well as the portion of undistributed earnings during the period allocable to participating securities.

New Accounting Pronouncements

Adoption of New Accounting Standards

On January 1, 2020, the Company adopted a new accounting standard issued by the Financial Accounting Standards Board ("FASB") which aligns the requirements for deferring implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The adoption of this standard, which the Company elected to do on a prospective basis, did not have a material impact on the Company's consolidated results of operations, financial position or cash flows.

On January 1, 2020, the Company adopted a new accounting standard issued by the FASB that changes the impairment model for most financial instruments, including trade receivables, from an incurred loss method to a new forward-looking approach, based on expected losses. The estimate of expected credit losses requires entities to incorporate considerations of historical information, current information and reasonable and supportable forecasts. The adoption of this new standard, which was done using a modified retrospective transition approach, did not have a material impact on the Company's consolidated results of operations, financial position or cash flows. See Note 15 for further details on the Company's allowance for credit losses policy.

New Accounting Standards to be Adopted

In March 2020, the FASB issued a new accounting standard which provides temporary optional guidance to ease the potential burden in accounting for reference rate reform due to the risk of cessation of the London Interbank Offered Rate ("LIBOR"). The amendments apply only to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. The pronouncement is effective immediately and can be applied through December 31, 2022. The adoption of this standard is not expected to have a material impact on the Company’s consolidated results of operations, financial position or cash flows.

Derivative Financial Instruments

The Company uses derivative financial instruments to manage its exposure to market risks for changes in interest rates and, from time to time, foreign currencies. This strategy includes the use of interest rate swap agreements, forward-starting interest rate swap agreements, treasury lock agreements and foreign currency forward contracts to manage its exposure to movements in interest and currency rates. The Company has established policies and procedures for risk assessment and the approval, reporting and monitoring of derivative financial instrument activities. These policies prohibit holding or issuing derivative financial instruments for speculative purposes. The Company does not enter into derivative financial instruments that contain credit-risk-related contingent features or requirements to post collateral.

Interest Rate Risk

The Company is exposed to interest rate risk on its cash and cash equivalents and its debt obligations. Interest income earned on cash and cash equivalents may fluctuate as interest rates change; however, due to their relatively short maturities, the Company does not hedge these assets or their investment cash flows and the impact of interest rate risk is not material. The Company's debt obligations consist of fixed-rate and variable-rate debt instruments. The Company's primary objective is to achieve the lowest overall cost of funding while managing the variability in cash outflows within an acceptable range. In order to achieve this objective, the Company enters into interest rate swaps.

Interest rate swaps involve the periodic exchange of payments without the exchange of underlying principal or notional amounts. Net settlements between the counterparties are recognized as an adjustment to interest expense.

Allowance for Credit Losses Policy

When estimating its allowance for credit losses, the Company pools its trade receivables based on the following customer types: healthcare insurers, government payers, client payers and patients.

For the healthcare insurers and government payers, collection of the Company’s net revenues is normally a function of providing the complete and correct billing information within the various filing deadlines, and provided that the Company has billed the payers accurately with complete information prior to the established filing deadline, there has historically been little to no collection risk.

Client payers primarily include physicians, hospitals, IDNs, ACOs, employers, other commercial laboratories and institutions for which services are performed on a wholesale basis and are billed based on negotiated fee schedules. Credit risk and ability to pay are more of a consideration for these payers.

With respect to patients, implicit price concessions, which represent differences between amounts billed and the estimated consideration the Company expects to receive from patients, are recognized as a reduction of revenue. Estimates of implicit price concessions consider historical collection experience (including the period the receivables have been outstanding) and other factors including current market conditions.

The Company principally estimates the allowance for credit losses by pool based on historical collection experience, the current credit worthiness of the customers, current economic conditions, expectations of future economic conditions and the period that the receivables have been outstanding. To the extent that any individual payers are identified that have deteriorated in credit quality, the Company removes the customers from their respective pools and establishes allowances based on the individual risk characteristics of such customers.

Although the Company believes that its estimates for contractual allowances and patient price concessions as well as its allowance for credit losses are appropriate, it is possible that the Company will experience an impact on cash collections as a result of the impact of the COVID-19 pandemic.