Business Overview and Summary of Significant Accounting Policies (Policy)	12 Months Ended
Dec. 31, 2022
Accounting Policies [Abstract]
Principles of Consolidation	The consolidated financial statements include the accounts of Fastenal Company and its subsidiaries (collectively, referred to as Fastenal or by terms such as we, our, or us). All material intercompany balances and transactions have been eliminated in consolidation.
Revenue Recognition	Net sales include products and shipping and handling charges, net of estimates for product returns and any related sales incentives. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring products. All revenue is recognized when we satisfy our performance obligations under the contract. We recognize revenue by transferring control of the promised products to the customer, with the majority of revenue recognized at the point in time the customer obtains control of the products. We recognize revenue for shipping and handling charges at the time the products are delivered to or picked up by the customer. We estimate product returns based on historical return rates. Using probability assessments, which are based on known inputs at year-end, we estimate sales incentives expected to be paid over the term of the contract. The majority of our contracts have a single performance obligation and are short term in nature. Sales taxes and value added taxes in foreign jurisdictions that are collected from customers and remitted to governmental authorities are accounted for on a net basis and therefore are excluded from net sales.
Accounts Receivable	Credit is extended based upon an evaluation of the customer's financial condition. Accounts receivable are stated at their estimated net realizable value. The allowance for credit losses is based on an income statement approach which adjusts the ending balance sheet to take into consideration expected losses over the contractual lives of the receivables, considering factors such as historical data as a basis for future expected losses.
Foreign Currency Translation and Transactions	The functional currency of our foreign operations is typically the applicable local currency. The functional currency is translated into United States dollars for balance sheet accounts, except retained earnings, using current exchange rates as of the balance sheet date, for retained earnings at historical exchange rates, and for revenue and expense accounts using a weighted average exchange rate during the applicable period. The translation adjustments are deferred as a separate component of stockholders' equity captioned accumulated other comprehensive income (loss). Gains or losses resulting from transactions denominated in foreign currencies are included in cost of sales or operating and administrative expenses.
Cash and Cash Equivalents	We consider all highly liquid investments purchased with original maturities of three months or less to be cash equivalents.
Inventories	Inventories, consisting of finished goods merchandise held for resale, are stated at the lower of cost (first in, first out method) or net realizable value. We record valuation adjustments for excess, slow-moving, and obsolete inventory that are equal to the difference between the cost and estimated net realizable value for that inventory. These estimates are based on a review and comparison of the current inventory levels to projected and historical sales of inventory.
Property and Equipment	Property and equipment are stated at cost. Depreciation on property and equipment is provided for using the straight-line method over the anticipated economic useful lives of the related property.
Leases	We determine if an arrangement contains a lease at inception. Operating leases are included in our operating lease right-of-use (ROU) assets, the current portion of operating lease liabilities, and the operating lease liabilities in our Consolidated Balance Sheets. The ROU assets represent our right to control the use of an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The operating lease ROU assets also include any prepaid lease payments made and exclude lease incentives. Lease expense is recognized on a straight-line basis over the lease term. Many of our leases include both lease (e.g., fixed payments including rent, taxes, and insurance costs) and non-lease components (e.g., common-area or other maintenance costs) which are accounted for as a single lease component as we have elected the practical expedient to group lease and non-lease components for all leases. Our pick-up truck leases typically have a non-cancelable lease term of less than one year and therefore, we have elected the practical expedient to exclude these short-term leases from our ROU assets and lease liabilities. Most leases include one or more options to renew. The exercise of lease renewal options is typically at our sole discretion; therefore, the majority of renewals to extend the lease terms are not included in our ROU assets and lease liabilities as they are not reasonably certain of exercise. We regularly evaluate the renewal options and when they are reasonably certain of exercise, we include the renewal period in our lease term. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the lease commencement date in determining the present value of the lease payments. We have a centrally managed treasury function; therefore, based on the applicable lease terms and the current economic environment, we apply a portfolio approach for determining the incremental borrowing rate.
Long-Lived Assets	Long-lived assets consist of net property and equipment, operating lease right-of-use assets, prepaid deposits, goodwill, and definite-lived intangible assets, and are reviewed for impairment whenever an event or change in circumstance indicates that the carrying amount of the asset may not be recoverable. If circumstances require a long-lived asset or asset group be tested for possible impairment, we first compare undiscounted cash flows expected to be generated by the asset or asset group to its carrying value. If the carrying value of the long-lived asset or asset group is not recoverable on an undiscounted cash flow basis, an impairment is recognized to the extent the carrying value exceeds its fair value. Fair value is determined through various valuation techniques including discounted cash flow models, quoted market values, and third-party independent appraisals, as necessary.
Long-Lived Assets (Goodwill and Other)	Goodwill represents the excess of the purchase price over the fair value of net assets acquired. Goodwill is reviewed for impairment annually. The identifiable intangible assets are amortized on a straight-line basis over their estimated life.
Accounting Estimates	The preparation of the consolidated financial statements in conformity with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and the disclosure of contingent liabilities. Actual results could differ from those estimates.
Insurance Reserves	We are self-insured for certain losses relating to workers' compensation, automobile, health, and general liability costs. Specific stop-loss coverage is provided for catastrophic claims in order to limit exposure to significant claims. Self-insurance liabilities are based on our estimate of reported claims and claims incurred but not yet reported.
Product Warranties	We offer a basic limited warranty for certain of our products. The specific terms and conditions of those warranties vary depending upon the product sold. We typically recoup these costs through product warranties we hold with the original equipment manufacturers. Our warranty expense has historically been minimal.
Stock-Based Compensation	We estimate the fair value of stock options as of the date of the grant using a Black-Scholes valuation model. Stock-based compensation expense equal to the grant date fair value is recognized on a straight-line basis over the vesting period. Our stock-based compensation expense is recorded in operating and administrative expenses.
Income Taxes	We account for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. We recognize the effect of income tax positions only if those positions are more likely than not to be sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. We record interest and penalties related to unrecognized tax benefits in income tax expense.
Earnings Per Share	Basic net earnings per share is calculated using net earnings available to common stockholders divided by the weighted average number of shares of common stock outstanding during the year. Diluted net earnings per share is similar to basic net earnings per share except that the weighted average number of shares of common stock outstanding includes the incremental shares assumed to be issued upon the exercise of stock options considered to be 'in-the-money' (i.e., when the market price of our stock is greater than the exercise price of our outstanding stock options).
Segment Reporting	We have determined that for our North American regions we meet the aggregation criteria outlined in the accounting standards as these regions have similar: (1) economic characteristics, (2) products and services, (3) customers, (4) distribution channels, and (5) regulatory environments. Considering our operations outside of North America represent less than 10% of our net sales, net earnings, or assets, we report as a single business segment.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In March 2020, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides temporary optional expedients and exceptions to U.S. GAAP on contract modifications, hedging relationships, and other transactions affected by reference rate reform to ease entities' financial reporting burdens as the market transitions from the London Interbank Offered Rate (LIBOR) and other interbank offered rates to alternative reference rates. The guidance was effective upon issuance and may be applied prospectively to contract modifications made, hedging relationships entered into, and other transactions affected by reference rate reform, evaluated on or before December 31, 2022, beginning during the reporting period in which the guidance has been elected. In December 2022, the FASB issued ASU 2022-06, Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848, which extended the date to December 31, 2024. We do not have any receivables, hedging relationships, lease agreements, or debt agreements that reference LIBOR or another reference rate expected to be discontinued. On September 28, 2022, we amended and restated our unsecured revolving credit agreement. At the same time, we also amended our master note agreement. As a result of those amendments, our floating rate debt no longer references a LIBOR based benchmark rate. Therefore, we will not be electing the optional practical expedients associated with this ASU.

Business Overview and Summary of Significant Accounting Policies (Policy)

12 Months Ended

Dec. 31, 2022

The consolidated financial statements include the accounts of Fastenal Company and its subsidiaries (collectively, referred to as Fastenal or by terms such as we, our, or us). All material intercompany balances and transactions have been eliminated in consolidation.

Revenue Recognition

Net sales include products and shipping and handling charges, net of estimates for product returns and any related sales incentives. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring products. All revenue is recognized when we satisfy our performance obligations under the contract. We recognize revenue by transferring control of the promised products to the customer, with the majority of revenue recognized at the point in time the customer obtains control of the products. We recognize revenue for shipping and handling charges at the time the products are delivered to or picked up by the customer. We estimate product returns based on historical return rates. Using probability assessments, which are based on known inputs at year-end, we estimate sales incentives expected to be paid over the term of the contract. The majority of our contracts have a single performance obligation and are short term in nature. Sales taxes and value added taxes in foreign jurisdictions that are collected from customers and remitted to governmental authorities are accounted for on a net basis and therefore are excluded from net sales.

Accounts Receivable

Credit is extended based upon an evaluation of the customer's financial condition. Accounts receivable are stated at their estimated net realizable value. The allowance for credit losses is based on an income statement approach which adjusts the ending balance sheet to take into consideration expected losses over the contractual lives of the receivables, considering factors such as historical data as a basis for future expected losses.

Foreign Currency Translation and Transactions

The functional currency of our foreign operations is typically the applicable local currency. The functional currency is translated into United States dollars for balance sheet accounts, except retained earnings, using current exchange rates as of the balance sheet date, for retained earnings at historical exchange rates, and for revenue and expense accounts using a weighted average exchange rate during the applicable period. The translation adjustments are deferred as a separate component of stockholders' equity captioned accumulated other comprehensive income (loss). Gains or losses resulting from transactions denominated in foreign currencies are included in cost of sales or operating and administrative expenses.

Cash and Cash Equivalents

We consider all highly liquid investments purchased with original maturities of three months or less to be cash equivalents.

Inventories

Inventories, consisting of finished goods merchandise held for resale, are stated at the lower of cost (first in, first out method) or net realizable value. We record valuation adjustments for excess, slow-moving, and obsolete inventory that are equal to the difference between the cost and estimated net realizable value for that inventory. These estimates are based on a review and comparison of the current inventory levels to projected and historical sales of inventory.

Property and Equipment

Property and equipment are stated at cost. Depreciation on property and equipment is provided for using the straight-line method over the anticipated economic useful lives of the related property.

Leases

We determine if an arrangement contains a lease at inception. Operating leases are included in our operating lease right-of-use (ROU) assets, the current portion of operating lease liabilities, and the operating lease liabilities in our Consolidated Balance Sheets.

The ROU assets represent our right to control the use of an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The operating lease ROU assets also include any prepaid lease payments made and exclude lease incentives. Lease expense is recognized on a straight-line basis over the lease term.

Many of our leases include both lease (e.g., fixed payments including rent, taxes, and insurance costs) and non-lease components (e.g., common-area or other maintenance costs) which are accounted for as a single lease component as we have elected the practical expedient to group lease and non-lease components for all leases. Our pick-up truck leases typically have a non-cancelable lease term of less than one year and therefore, we have elected the practical expedient to exclude these short-term leases from our ROU assets and lease liabilities.

Most leases include one or more options to renew. The exercise of lease renewal options is typically at our sole discretion; therefore, the majority of renewals to extend the lease terms are not included in our ROU assets and lease liabilities as they are not reasonably certain of exercise. We regularly evaluate the renewal options and when they are reasonably certain of exercise, we include the renewal period in our lease term.

As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the lease commencement date in determining the present value of the lease payments. We have a centrally managed treasury function; therefore, based on the applicable lease terms and the current economic environment, we apply a portfolio approach for determining the incremental borrowing rate.

Long-Lived Assets

Long-lived assets consist of net property and equipment, operating lease right-of-use assets, prepaid deposits, goodwill, and definite-lived intangible assets, and are reviewed for impairment whenever an event or change in circumstance indicates that the carrying amount of the asset may not be recoverable. If circumstances require a long-lived asset or asset group be tested for possible impairment, we first compare undiscounted cash flows expected to be generated by the asset or asset group to its carrying value. If the carrying value of the long-lived asset or asset group is not recoverable on an undiscounted cash flow basis, an impairment is recognized to the extent the carrying value exceeds its fair value. Fair value is determined through various valuation techniques including discounted cash flow models, quoted market values, and third-party independent appraisals, as necessary.

Long-Lived Assets (Goodwill and Other)

Goodwill represents the excess of the purchase price over the fair value of net assets acquired. Goodwill is reviewed for impairment annually. The identifiable intangible assets are amortized on a straight-line basis over their estimated life.

Accounting Estimates

The preparation of the consolidated financial statements in conformity with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and the disclosure of contingent liabilities. Actual results could differ from those estimates.

Insurance Reserves

We are self-insured for certain losses relating to workers' compensation, automobile, health, and general liability costs. Specific stop-loss coverage is provided for catastrophic claims in order to limit exposure to significant claims. Self-insurance liabilities are based on our estimate of reported claims and claims incurred but not yet reported.

Product Warranties

We offer a basic limited warranty for certain of our products. The specific terms and conditions of those warranties vary depending upon the product sold. We typically recoup these costs through product warranties we hold with the original equipment manufacturers. Our warranty expense has historically been minimal.

Stock-Based Compensation

We estimate the fair value of stock options as of the date of the grant using a Black-Scholes valuation model. Stock-based compensation expense equal to the grant date fair value is recognized on a straight-line basis over the vesting period. Our stock-based compensation expense is recorded in operating and administrative expenses.

Income Taxes

We account for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date.

We recognize the effect of income tax positions only if those positions are more likely than not to be sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. We record interest and penalties related to unrecognized tax benefits in income tax expense.

Earnings Per Share

Basic net earnings per share is calculated using net earnings available to common stockholders divided by the weighted average number of shares of common stock outstanding during the year. Diluted net earnings per share is similar to basic net earnings per share except that the weighted average number of shares of common stock outstanding includes the incremental shares assumed to be issued upon the exercise of stock options considered to be 'in-the-money' (i.e., when the market price of our stock is greater than the exercise price of our outstanding stock options).

Segment Reporting

We have determined that for our North American regions we meet the aggregation criteria outlined in the accounting standards as these regions have similar: (1) economic characteristics, (2) products and services, (3) customers, (4) distribution channels, and (5) regulatory environments. Considering our operations outside of North America represent less than 10% of our net sales, net earnings, or assets, we report as a single business segment.

Recently Issued Accounting Pronouncements

In March 2020, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides temporary optional expedients and exceptions to U.S. GAAP on contract modifications, hedging relationships, and other transactions affected by reference rate reform to ease entities' financial reporting burdens as the market transitions from the London Interbank Offered Rate (LIBOR) and other interbank offered rates to alternative reference rates. The guidance was effective upon issuance and may be applied prospectively to contract modifications made, hedging relationships entered into, and other transactions affected by reference rate reform, evaluated on or before December 31, 2022, beginning during the reporting period in which the guidance has been elected. In December 2022, the FASB issued ASU 2022-06, Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848, which extended the date to December 31, 2024. We do not have any receivables, hedging relationships, lease agreements, or debt agreements that reference LIBOR or another reference rate expected to be discontinued. On September 28, 2022, we amended and restated our unsecured revolving credit agreement. At the same time, we also amended our master note agreement. As a result of those amendments, our floating rate debt no longer references a LIBOR based benchmark rate. Therefore, we will not be electing the optional practical expedients associated with this ASU.