Summary of Significant Accounting Policies (Policy)	12 Months Ended
Dec. 31, 2023
Accounting Policies [Abstract]
Consolidation	Consolidation - Our consolidated financial statements include the accounts of NewMarket Corporation and its subsidiaries. All intercompany transactions are eliminated upon consolidation. References to "we," "us," "our," the "company," and "NewMarket" are to NewMarket Corporation and its consolidated subsidiaries, unless the context indicates otherwise. NewMarket is the parent company of separate operating companies, each managing its own assets and liabilities. Those companies are Afton, which focuses on petroleum additive products; Ethyl, representing certain contracted manufacturing and related services, as well as the antiknock compounds business; and NewMarket Development, which manages the real property and improvements that we own in Virginia. NewMarket is also the parent company of NewMarket Services, which provides various administrative services to NewMarket, Afton, Ethyl, and NewMarket Development.
Foreign Currency Translation	Foreign Currency Translation - We translate the balance sheets of our foreign subsidiaries into U.S. Dollars based on the current exchange rate at the end of each period. We translate the statements of income using the weighted-average exchange rates for the period. NewMarket includes translation adjustments in the Consolidated Balance Sheets as part of accumulated other comprehensive loss and transaction adjustments in the Consolidated Statements of Income as part of cost of goods sold.
Revenue Recognition	Revenue Recognition - We recognize revenue when control of the product is transferred to our customer and for an amount that reflects the consideration we expect to collect from the customer. Net sales (revenues) are reported at the gross amount billed, including amounts related to shipping that are charged to the customer. Provisions for rebates to customers are recorded in the same period that the related sales are recorded. Freight costs incurred on the delivery of products are included in the Consolidated Statements of Income in cost of goods sold. Our standard terms of delivery are included in our contracts, sales order confirmation documents, and invoices. Taxes assessed by a governmental authority concurrent with sales to our customers, including sales, use, value-added, and revenue-related excise taxes, are not included as net sales, but are reflected in accrued expenses until remitted to the appropriate governmental authority.
Cash and Cash Equivalents	Cash and Cash Equivalents - Our cash equivalents consist of government obligations and commercial paper with original maturities of less than 90 days. Throughout the year, we have cash balances in excess of federally insured amounts on deposit with various financial institutions. We state cash and cash equivalents at cost, which approximates fair value.
Marketable Securities, Policy	Marketable Securities - Our trading and equity securities are recorded at estimated fair value. Unrealized gains and losses on trading and equity securities are included in net income.
Accounts Receivable	Accounts Receivable - We record our accounts receivable at invoiced amounts adjusted for allowances for credit losses. The allowance for credit losses represents probable losses to be incurred if our customers do not make required payments. We determine the adequacy of the allowance by periodically evaluating each customer’s receivable balance, considering their financial condition and credit history, and considering current economic conditions. The allowance for credit losses was not material at December 31, 2023 or December 31, 2022.
Inventories	Inventories - NewMarket values its inventories at the lower of cost or net realizable value. In the United States, petroleum additives inventory cost is determined on the last-in, first-out (LIFO) basis. For all other inventory, we determine cost using a weighted-average method. Inventory cost includes raw materials, direct labor, and manufacturing overhead.
Property, Plant, and Equipment	Property, Plant, and Equipment - We state property, plant, and equipment at cost less accumulated depreciation and compute depreciation by the straight-line method based on the estimated useful lives of the assets. We capitalize expenditures for significant improvements that extend the useful life of the related property. We expense repairs and maintenance, including plant turnaround costs, as incurred. When property is sold or retired, we remove the cost and accumulated depreciation from the accounts and any related gain or loss is included in earnings.
Intangibles (Net of Amortization) and Goodwill	Intangibles (Net of Amortization) and Goodwill - Identifiable intangibles include acquired contracts, formulas and technology, trademarks and trade names, and customer bases. We assign a value to acquired identifiable intangibles based on independent third-party appraisals and management's assessment at the time of acquisition. NewMarket amortizes the cost of the customer bases by an accelerated method and the cost of the remaining identifiable intangibles by the straight-line method over the estimated economic life of the intangible. Goodwill arises from the excess of cost over the net assets of businesses acquired. Goodwill represents the residual purchase price after allocation to all identifiable net assets. We test goodwill for impairment each year, as well as whenever a significant event or circumstance occurs which could reduce the fair value of the reporting unit to which the goodwill applies below the carrying amount of the reporting unit.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets - When significant events or circumstances occur that might impair the value of long-lived assets, we evaluate recoverability of the recorded cost of these assets. Assets are considered to be impaired if their carrying amount is not recoverable from the estimated undiscounted future cash flows associated with the assets. If we determine an asset is impaired and its recorded cost is higher than estimated fair value based on the estimated present value of future cash flows, we adjust the asset to the estimated fair value.
Environmental Costs	Environmental Costs - NewMarket capitalizes environmental compliance costs if they extend the useful life of the related property or prevent future contamination. Environmental compliance costs also include maintenance and operation of pollution prevention and control facilities. We expense these compliance costs in cost of goods sold as incurred. Accrued environmental remediation and monitoring costs relate to an existing condition caused by past operations. NewMarket accrues these costs in current operations within cost of goods sold in the Consolidated Statements of Income when it is probable that we have incurred a liability and the amount can be reasonably estimated. These estimates are based on an assessment of the site, available clean-up methods, and prior experience in handling remediation. When we can reliably determine the amount and timing of future cash flows, we discount these liabilities, incorporating an inflation factor.
Legal Costs	Legal Costs - We expense legal costs in the period incurred.
Employee Savings Plan	Employee Savings Plan - Most of our full-time salaried and hourly employees may participate in defined contribution savings plans. Employees who are covered by collective bargaining agreements may also participate in a savings plan according to the terms of their bargaining agreements. Employees, as well as NewMarket, contribute to the plans.
Research, Development, and Testing Expenses	Research, Development, and Testing Expenses - NewMarket expenses all research, development, and testing costs as incurred. R&D costs include personnel-related costs, as well as internal and external testing of our products.
Income Taxes	Income Taxes - We recognize deferred income taxes for temporary differences between the financial reporting basis and the income tax basis of assets and liabilities. We also adjust for changes in tax rates and laws at the time the changes are enacted. A valuation allowance is recorded when it is more likely than not that a deferred tax asset will not be realized. We typically remove a tax impact from accumulated other comprehensive loss when the underlying circumstance which gave rise to the tax impact no longer exists. The calculation of income tax liabilities involves uncertainties in the application of complex tax laws and regulations, which are subject to legal interpretation and management judgment. Our income tax returns are regularly examined by federal, state and foreign tax authorities, and those audits may result in proposed adjustments. We have evaluated our tax positions under the more likely than not standard of the accounting literature, and a tax position is recognized if it meets this standard. Such judgments and estimates may change based on audit settlements, court cases, and interpretation of tax laws and regulations. We recognize accrued interest and penalties associated with uncertain tax positions as part of income tax expense on our Consolidated Statements of Income.
Leases	Leases - We determine if an arrangement includes a lease at the inception of the agreement. The right-of-use asset and lease liability are determined at the lease commencement date and are based on the present value of estimated lease payments. Our lease agreements contain both fixed and variable lease payments. In some cases, variable lease payments are based on a rate or an index. Fixed lease payments, as well as variable lease payments which are based on a rate or index, are included in the determination of the right-of-use asset and lease liability at lease inception. Variable lease payments that are not based on a rate or index are expensed when incurred. The present value of estimated lease payments is determined utilizing the rate implicit in the lease agreement if that rate can be determined. If the implicit rate cannot be determined, the present value of estimated lease payments is determined utilizing our incremental borrowing rate. The incremental borrowing rate is determined at the lease commencement date and is developed utilizing a readily available market interest rate curve adjusted for our credit quality. Some of our leases include an option to renew that can extend the lease term. For those leases which are reasonably certain to be renewed, we include the renewal in the lease term. We do not recognize leases with terms of 12 months or less on the balance sheet for any lease class, except the railcar lease class. For the short-term leases not recorded on the balance sheet, the lease payments are recognized in the Consolidated Statements of Income on a straight-line basis over the lease term. We account for the lease and nonlease components as a single lease component in determining the right-of-use assets and lease liabilities for all lease classes.
Derivative Financial Instruments and Hedging Activities	Derivative Financial Instruments and Hedging Activities - We are exposed to certain risks arising from both our business operations and economic conditions. We manage our exposures to a wide variety of business and operational risks through management of our core business activities. We manage certain economic risks, including interest rate, liquidity, and credit risk primarily by managing the amount, sources, and duration of our debt funding, as well as through the use of derivative financial instruments. We sometimes enter into interest rate swaps to manage our exposure to interest rate movements. In addition, our foreign operations expose us to fluctuations of foreign exchange rates. These fluctuations may impact our results of operations, financial position, and cash flows. To manage this exposure, we sometimes enter into foreign currency forward contracts to minimize currency exposure due to cash flows from foreign operations. We record all derivatives on the balance sheet at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether we have elected to designate a derivative in a hedging relationship and apply hedge accounting, and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. We may enter into derivative contracts that are intended to economically hedge certain of our risks, even though hedge accounting does not apply, or we elect not to apply hedge accounting. We do not enter into derivative instruments for speculative purposes. We had no derivative financial instruments outstanding at December 31, 2023 or December 31, 2022.
Stock-based Compensation	Stock-based Compensation - We calculate the fair value of restricted stock and restricted stock units based on the closing price of our common stock on the date of grant. If award recipients are entitled to receive dividends during the vesting period, we make no adjustment to the fair value of the award for dividends. If the award does not entitle recipients to dividends during the vesting period, we reduce the grant-date price of our common stock by the present value of the dividends expected to be paid on the underlying shares during the vesting period, discounted at the risk-free interest rate. We recognize stock-based compensation expense for the number of awards expected to vest on a straight-line basis over the requisite service period.
Estimates and Risks Due to Concentration of Business	Estimates and Risks Due to Concentration of Business - The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. In addition, our financial results can be influenced by certain risk factors. Some of our significant concentrations of risk include the following: •reliance on a small number of significant customers; •customers concentrated in the fuel and lubricant industries; and •production of several of our products solely at one facility.
Debt, Policy [Policy Text Block]	Long-term debt - We record the carrying amount of our long-term debt at historical cost, less deferred financing costs related to our outstanding senior notes.
Fair Value Measurement, Policy [Policy Text Block]	Long-term debt - We record the carrying amount of our long-term debt at historical cost, less deferred financing costs related to our outstanding senior notes.

Summary of Significant Accounting Policies (Policy)

12 Months Ended

Dec. 31, 2023

Consolidation - Our consolidated financial statements include the accounts of NewMarket Corporation and its subsidiaries. All intercompany transactions are eliminated upon consolidation. References to "we," "us," "our," the "company," and "NewMarket" are to NewMarket Corporation and its consolidated subsidiaries, unless the context indicates otherwise.

NewMarket is the parent company of separate operating companies, each managing its own assets and liabilities. Those companies are Afton, which focuses on petroleum additive products; Ethyl, representing certain contracted manufacturing and related services, as well as the antiknock compounds business; and NewMarket Development, which manages the real property and improvements that we own in Virginia. NewMarket is also the parent company of NewMarket Services, which provides various administrative services to NewMarket, Afton, Ethyl, and NewMarket Development.

Foreign Currency Translation

Foreign Currency Translation - We translate the balance sheets of our foreign subsidiaries into U.S. Dollars based on the current exchange rate at the end of each period. We translate the statements of income using the weighted-average exchange rates for the period. NewMarket includes translation adjustments in the Consolidated Balance Sheets as part of accumulated other comprehensive loss and transaction adjustments in the Consolidated Statements of Income as part of cost of goods sold.

Revenue Recognition

Revenue Recognition - We recognize revenue when control of the product is transferred to our customer and for an amount that reflects the consideration we expect to collect from the customer. Net sales (revenues) are reported at the gross amount billed, including amounts related to shipping that are charged to the customer. Provisions for rebates to customers are recorded in the same period that the related sales are recorded. Freight costs incurred on the delivery of products are included in the Consolidated Statements of Income in cost of goods sold. Our standard terms of delivery are included in our contracts, sales order confirmation documents, and invoices. Taxes assessed by a governmental authority concurrent with sales to our customers, including sales, use, value-added, and revenue-related excise taxes, are not included as net sales, but are reflected in accrued expenses until remitted to the appropriate governmental authority.

Cash and Cash Equivalents

Cash and Cash Equivalents - Our cash equivalents consist of government obligations and commercial paper with original maturities of less than 90 days. Throughout the year, we have cash balances in excess of federally insured amounts on deposit with various financial institutions. We state cash and cash equivalents at cost, which approximates fair value.

Marketable Securities, Policy

Marketable Securities - Our trading and equity securities are recorded at estimated fair value. Unrealized gains and losses on trading and equity securities are included in net income.

Accounts Receivable

Accounts Receivable - We record our accounts receivable at invoiced amounts adjusted for allowances for credit losses. The allowance for credit losses represents probable losses to be incurred if our customers do not make required payments. We determine the adequacy of the allowance by periodically evaluating each customer’s receivable balance, considering their financial condition and credit history, and considering current economic conditions. The allowance for credit losses was not material at December 31, 2023 or December 31, 2022.

Inventories

Inventories - NewMarket values its inventories at the lower of cost or net realizable value. In the United States, petroleum additives inventory cost is determined on the last-in, first-out (LIFO) basis. For all other inventory, we determine cost using a weighted-average method. Inventory cost includes raw materials, direct labor, and manufacturing overhead.

Property, Plant, and Equipment

Property, Plant, and Equipment - We state property, plant, and equipment at cost less accumulated depreciation and compute depreciation by the straight-line method based on the estimated useful lives of the assets. We capitalize expenditures for significant improvements that extend the useful life of the related property. We expense repairs and maintenance, including plant turnaround costs, as incurred. When property is sold or retired, we remove the cost and accumulated depreciation from the accounts and any related gain or loss is included in earnings.

Intangibles (Net of Amortization) and Goodwill

Intangibles (Net of Amortization) and Goodwill - Identifiable intangibles include acquired contracts, formulas and technology, trademarks and trade names, and customer bases. We assign a value to acquired identifiable intangibles based on independent third-party appraisals and management's assessment at the time of acquisition. NewMarket amortizes the cost of the customer bases by an accelerated method and the cost of the remaining identifiable intangibles by the straight-line method over the estimated economic life of the intangible.

Goodwill arises from the excess of cost over the net assets of businesses acquired. Goodwill represents the residual purchase price after allocation to all identifiable net assets. We test goodwill for impairment each year, as well as whenever a significant event or circumstance occurs which could reduce the fair value of the reporting unit to which the goodwill applies below the carrying amount of the reporting unit.

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets - When significant events or circumstances occur that might impair the value of long-lived assets, we evaluate recoverability of the recorded cost of these assets. Assets are considered to be impaired if their carrying amount is not recoverable from the estimated undiscounted future cash flows associated with the assets. If we determine an asset is impaired and its recorded cost is higher than estimated fair value based on the estimated present value of future cash flows, we adjust the asset to the estimated fair value.

Environmental Costs

Environmental Costs - NewMarket capitalizes environmental compliance costs if they extend the useful life of the related property or prevent future contamination. Environmental compliance costs also include maintenance and operation of pollution prevention and control facilities. We expense these compliance costs in cost of goods sold as incurred.

Accrued environmental remediation and monitoring costs relate to an existing condition caused by past operations. NewMarket accrues these costs in current operations within cost of goods sold in the Consolidated Statements of Income when it is probable that we have incurred a liability and the amount can be reasonably estimated. These estimates are based on an assessment of the site, available clean-up methods, and prior experience in handling remediation.

When we can reliably determine the amount and timing of future cash flows, we discount these liabilities, incorporating an inflation factor.

Legal Costs

Legal Costs - We expense legal costs in the period incurred.

Employee Savings Plan

Employee Savings Plan - Most of our full-time salaried and hourly employees may participate in defined contribution savings plans. Employees who are covered by collective bargaining agreements may also participate in a savings plan according to the terms of their bargaining agreements. Employees, as well as NewMarket, contribute to the plans.

Research, Development, and Testing Expenses

Research, Development, and Testing Expenses - NewMarket expenses all research, development, and testing costs as incurred. R&D costs include personnel-related costs, as well as internal and external testing of our products.

Income Taxes

Income Taxes - We recognize deferred income taxes for temporary differences between the financial reporting basis and the income tax basis of assets and liabilities. We also adjust for changes in tax rates and laws at the time the changes are enacted. A valuation allowance is recorded when it is more likely than not that a deferred tax asset will not be realized. We typically remove a tax impact from accumulated other comprehensive loss when the underlying circumstance which gave rise to the tax impact no longer exists.

The calculation of income tax liabilities involves uncertainties in the application of complex tax laws and regulations, which are subject to legal interpretation and management judgment. Our income tax returns are regularly examined by federal, state and foreign tax authorities, and those audits may result in proposed adjustments. We have evaluated our tax positions under the more likely than not standard of the accounting literature, and a tax position is recognized if it meets this standard. Such judgments and estimates may change based on audit settlements, court cases, and interpretation of tax laws and regulations. We recognize accrued interest and penalties associated with uncertain tax positions as part of income tax expense on our Consolidated Statements of Income.

Leases

Leases - We determine if an arrangement includes a lease at the inception of the agreement. The right-of-use asset and lease liability are determined at the lease commencement date and are based on the present value of estimated lease payments.

Our lease agreements contain both fixed and variable lease payments. In some cases, variable lease payments are based on a rate or an index. Fixed lease payments, as well as variable lease payments which are based on a rate or index, are included in the determination of the right-of-use asset and lease liability at lease inception. Variable lease payments that are not based on a rate or index are expensed when incurred.

The present value of estimated lease payments is determined utilizing the rate implicit in the lease agreement if that rate can be determined. If the implicit rate cannot be determined, the present value of estimated lease payments is determined utilizing our incremental borrowing rate. The incremental borrowing rate is determined at the lease commencement date and is developed utilizing a readily available market interest rate curve adjusted for our credit quality.

Some of our leases include an option to renew that can extend the lease term. For those leases which are reasonably certain to be renewed, we include the renewal in the lease term.

We do not recognize leases with terms of 12 months or less on the balance sheet for any lease class, except the railcar lease class. For the short-term leases not recorded on the balance sheet, the lease payments are recognized in the Consolidated Statements of Income on a straight-line basis over the lease term.

We account for the lease and nonlease components as a single lease component in determining the right-of-use assets and lease liabilities for all lease classes.

Derivative Financial Instruments and Hedging Activities

Derivative Financial Instruments and Hedging Activities - We are exposed to certain risks arising from both our business operations and economic conditions. We manage our exposures to a wide variety of business and operational risks through management of our core business activities.

We manage certain economic risks, including interest rate, liquidity, and credit risk primarily by managing the amount, sources, and duration of our debt funding, as well as through the use of derivative financial instruments. We sometimes enter into interest rate swaps to manage our exposure to interest rate movements.

In addition, our foreign operations expose us to fluctuations of foreign exchange rates. These fluctuations may impact our results of operations, financial position, and cash flows. To manage this exposure, we sometimes enter into foreign currency forward contracts to minimize currency exposure due to cash flows from foreign operations.

We record all derivatives on the balance sheet at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether we have elected to designate a derivative in a hedging relationship and apply hedge accounting, and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. We may enter into derivative contracts that are intended to economically hedge certain of our risks, even though hedge accounting does not apply, or we elect not to apply hedge accounting. We do not enter into derivative instruments for speculative purposes. We had no derivative financial instruments outstanding at December 31, 2023 or December 31, 2022.

Stock-based Compensation

Stock-based Compensation - We calculate the fair value of restricted stock and restricted stock units based on the closing price of our common stock on the date of grant. If award recipients are entitled to receive dividends during the vesting period, we make no adjustment to the fair value of the award for dividends. If the award does not entitle recipients to dividends during the vesting period, we reduce the grant-date price of our common stock by the present value of the dividends expected to be paid on the underlying shares during the vesting period, discounted at the risk-free interest rate.

We recognize stock-based compensation expense for the number of awards expected to vest on a straight-line basis over the requisite service period.

Estimates and Risks Due to Concentration of Business

Estimates and Risks Due to Concentration of Business - The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and

assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.

In addition, our financial results can be influenced by certain risk factors. Some of our significant concentrations of risk include the following:

•reliance on a small number of significant customers;

•customers concentrated in the fuel and lubricant industries; and

•production of several of our products solely at one facility.

Debt, Policy [Policy Text Block]

Long-term debt - We record the carrying amount of our long-term debt at historical cost, less deferred financing costs related to our outstanding senior notes.

Fair Value Measurement, Policy [Policy Text Block]

Long-term debt - We record the carrying amount of our long-term debt at historical cost, less deferred financing costs related to our outstanding senior notes.