Summary of Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial statements that permit reduced disclosure for interim periods. In the opinion of management, the accompanying unaudited consolidated financial statements include all adjustments necessary for the fair presentation of our consolidated balance sheets as of March 31, 2019 and December 31, 2018, our consolidated statements of income for the three months ended March 31, 2019 and 2018, our consolidated statements of stockholders’ equity for the three months ended March 31, 2019 and 2018 and our consolidated statements of cash flows for the three months ended March 31, 2019 and 2018. Such adjustments are of a normal recurring nature. The information in this Quarterly Report on Form 10-Q (this “Form 10-Q”) should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2018 that was filed with the SEC on February 14, 2019 (the “Form 10-K”). The results of operations for the three months ended March 31, 2019 are not necessarily indicative of the results expected for the full year.
Reclassifications	Reclassifications Certain prior period amounts have been reclassified to conform to the current period presentation. These reclassifications had no impact on reported net income and did not result in any material change to operating cash flows. In addition to these adjustments, in the consolidated balance sheets, we combined the line items “Intangible assets, net” and “Other assets” in the prior period in order to conform to the current period presentation.
Recently Adopted New Accounting Pronouncements	Recently Adopted New Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, “Leases (Topic 842).” The purpose of this new guidance is to increase the transparency and comparability among organizations by recognizing lease assets and lease liabilities in the consolidated balance sheets as well as providing additional disclosure requirements related to leasing arrangements. The new guidance was effective for us beginning January 1, 2019, which we adopted using a modified retrospective method and the transition relief guidance provided by the FASB in ASU 2018-11. Under this adoption method, we have not restated comparative prior periods and have carried forward the assessment of whether our contracts are or contain leases, the classification of our leases and the remaining lease terms. Based on our portfolio of leases at January 1, 2019, $21.6 million of lease assets and liabilities were recognized in our consolidated balance sheets, which related to operating leases for real estate. Under the transition relief guidance, we have elected the lease vs. non-lease components practical expedient relating to the asset class of real estate, the short-term lease exemption practical expedient and the package of practical expedients. In connection with the adoption of this standard, we updated our control framework and implemented changes to existing controls to account for leases. See “Note 6. Leases” for additional information.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates include income taxes, loss contingencies, the useful life of property and equipment and intangible assets, the life of our client relationships, the fair value of our stock-based awards and the fair value of our financial instruments, intangible assets and goodwill. These estimates are based on historical experience where applicable and other assumptions that management believes are reasonable under the circumstances. Actual results could materially differ from these estimates.
Seasonality	Seasonality Our revenues are seasonal in nature. Recurring revenues include revenues relating to the annual processing of payroll forms, such as Form W-2, Form 1099, and Form 1095 and revenues from processing unscheduled payroll runs (such as bonuses) for our clients. As payroll forms are typically processed in the first quarter of the year, first quarter revenues and margins are generally higher than in subsequent quarters. These seasonal fluctuations in revenues can also have an impact on gross profits. Historical results impacted by these seasonal trends should not be considered a reliable indicator of our future results of operations.
Employee Stock Purchase Plan	Employee Stock Purchase Plan An award issued under the Paycom Software, Inc. Employee Stock Purchase Plan (the “ESPP”) is classified as a share-based liability and recognized at the fair value of the award. Expense is recognized, net of estimated forfeitures, on a straight-line basis over the requisite service period.
Funds Held for Clients and Client Funds Obligation	Funds Held for Clients and Client Funds Obligation As part of our payroll and tax filing application, we (i) collect client funds to satisfy their respective federal, state and local employment tax obligations, (ii) remit such funds to the appropriate taxing authorities and accounts designated by our clients, and (iii) manage client tax filings and any related correspondence with taxing authorities. Amounts collected by us from clients for their federal, state and local employment taxes are invested by us, and we earn interest on these funds during the interval between receipt and disbursement. These investments are shown in our consolidated balance sheets as funds held for clients, and the offsetting liability for the tax filings is shown as client funds obligation. The liability is recognized in the accompanying consolidated balance sheets at the time we obtain the funds from clients. The client funds obligation represents liabilities that will be repaid within one year of the consolidated balance sheet date. As of March 31, 2019 and December 31, 2018, the funds held for clients were invested in money market funds, demand deposit accounts, commercial paper and certificates of deposit. Short-term investments in commercial paper and certificates of deposit with an original maturity duration greater than three months are classified as available-for-sale securities, and are also included within the funds held for clients line item in the consolidated balance sheets. These available-for-sale securities are recognized in the consolidated balance sheets at fair value, which approximates the amortized cost of the securities. Funds held for clients are classified as a current asset in the consolidated balance sheets because the funds are held solely to satisfy the client funds obligation.
Stock Repurchase Plan	Stock Repurchase Plan In May 2016, our Board of Directors authorized a stock repurchase plan allowing for the repurchase of shares of our common stock in open market transactions at prevailing market prices, in privately negotiated transactions or by other means in accordance with federal securities laws, including Rule 10b5-1 programs. Since the initial authorization of the stock repurchase plan, our Board of Directors has amended and extended and authorized new stock repurchase plans from time to time. On February 13, 2018, we announced that our Board of Directors authorized the repurchase of up to an additional $100.0 million of common stock. Most recently, on November 20, 2018, we announced that our Board of Directors authorized the repurchase of up to an additional $150.0 million of our common stock. As of March 31, 2019, there was $142.3 million available for repurchases. Our stock repurchase plan may be suspended or discontinued at any time. The actual timing, number and value of shares repurchased depends on a number of factors, including the market price of our common stock, general market and economic conditions, shares withheld for taxes associated with the vesting of restricted stock and other corporate considerations. The current stock repurchase plan will expire on November 19, 2020. During the three months ended March 31, 2019, we repurchased an aggregate of 110,054 shares of our common stock at an average cost of $178.72 per share to satisfy tax withholding obligations for certain employees upon the vesting of restricted stock.
Recent Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements Management has reviewed all the recently issued, but not yet effective, accounting pronouncements, and does not believe any of these pronouncements will have a material impact to the Company.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2019

The accompanying unaudited interim consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial statements that permit reduced disclosure for interim periods. In the opinion of management, the accompanying unaudited consolidated financial statements include all adjustments necessary for the fair presentation of our consolidated balance sheets as of March 31, 2019 and December 31, 2018, our consolidated statements of income for the three months ended March 31, 2019 and 2018, our consolidated statements of stockholders’ equity for the three months ended March 31, 2019 and 2018 and our consolidated statements of cash flows for the three months ended March 31, 2019 and 2018. Such adjustments are of a normal recurring nature. The information in this Quarterly Report on Form 10-Q (this “Form 10-Q”) should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2018 that was filed with the SEC on February 14, 2019 (the “Form 10-K”). The results of operations for the three months ended March 31, 2019 are not necessarily indicative of the results expected for the full year.

Reclassifications

Certain prior period amounts have been reclassified to conform to the current period presentation. These reclassifications had no impact on reported net income and did not result in any material change to operating cash flows. In addition to these adjustments, in the consolidated balance sheets, we combined the line items “Intangible assets, net” and “Other assets” in the prior period in order to conform to the current period presentation.

Recently Adopted New Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, “Leases (Topic 842).” The purpose of this new guidance is to increase the transparency and comparability among organizations by recognizing lease assets and lease liabilities in the consolidated balance sheets as well as providing additional disclosure requirements related to leasing arrangements. The new guidance was effective for us beginning January 1, 2019, which we adopted using a modified retrospective method and the transition relief guidance provided by the FASB in ASU 2018-11. Under this adoption method, we have not restated comparative prior periods and have carried forward the assessment of whether our contracts are or contain leases, the classification of our leases and the remaining lease terms. Based on our portfolio of leases at January 1, 2019, $21.6 million of lease assets and liabilities were recognized in our consolidated balance sheets, which related to operating leases for real estate. Under the transition relief guidance, we have elected the lease vs. non-lease components practical expedient relating to the asset class of real estate, the short-term lease exemption practical expedient and the package of practical expedients. In connection with the adoption of this standard, we updated our control framework and implemented changes to existing controls to account for leases. See “Note 6. Leases” for additional information.

Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates include income taxes, loss contingencies, the useful life of property and equipment and intangible assets, the life of our client relationships, the fair value of our stock-based awards and the fair value of our financial instruments, intangible assets and goodwill. These estimates are based on historical experience where applicable and other assumptions that management believes are reasonable under the circumstances. Actual results could materially differ from these estimates.

Seasonality

Our revenues are seasonal in nature. Recurring revenues include revenues relating to the annual processing of payroll forms, such as Form W-2, Form 1099, and Form 1095 and revenues from processing unscheduled payroll runs (such as bonuses) for our clients. As payroll forms are typically processed in the first quarter of the year, first quarter revenues and margins are generally higher than in subsequent quarters. These seasonal fluctuations in revenues can also have an impact on gross profits. Historical results impacted by these seasonal trends should not be considered a reliable indicator of our future results of operations.

Employee Stock Purchase Plan

An award issued under the Paycom Software, Inc. Employee Stock Purchase Plan (the “ESPP”) is classified as a share-based liability and recognized at the fair value of the award. Expense is recognized, net of estimated forfeitures, on a straight-line basis over the requisite service period.

Funds Held for Clients and Client Funds Obligation

As part of our payroll and tax filing application, we (i) collect client funds to satisfy their respective federal, state and local employment tax obligations, (ii) remit such funds to the appropriate taxing authorities and accounts designated by our clients, and (iii) manage client tax filings and any related correspondence with taxing authorities. Amounts collected by us from clients for their federal, state and local employment taxes are invested by us, and we earn interest on these funds during the interval between receipt and disbursement.

These investments are shown in our consolidated balance sheets as funds held for clients, and the offsetting liability for the tax filings is shown as client funds obligation. The liability is recognized in the accompanying consolidated balance sheets at the time we obtain the funds from clients. The client funds obligation represents liabilities that will be repaid within one year of the consolidated balance sheet date. As of March 31, 2019 and December 31, 2018, the funds held for clients were invested in money market funds, demand deposit accounts, commercial paper and certificates of deposit. Short-term investments in commercial paper and certificates of deposit with an original maturity duration greater than three months are classified as available-for-sale securities, and are also included within the funds held for clients line item in the consolidated balance sheets. These available-for-sale securities are recognized in the consolidated balance sheets at fair value, which approximates the amortized cost of the securities. Funds held for clients are classified as a current asset in the consolidated balance sheets because the funds are held solely to satisfy the client funds obligation.

Stock Repurchase Plan

In May 2016, our Board of Directors authorized a stock repurchase plan allowing for the repurchase of shares of our common stock in open market transactions at prevailing market prices, in privately negotiated transactions or by other means in accordance with federal securities laws, including Rule 10b5-1 programs. Since the initial authorization of the stock repurchase plan, our Board of Directors has amended and extended and authorized new stock repurchase plans from time to time. On February 13, 2018, we announced that our Board of Directors authorized the repurchase of up to an additional $100.0 million of common stock. Most recently, on November 20, 2018, we announced that our Board of Directors authorized the repurchase of up to an additional $150.0 million of our common stock. As of March 31, 2019, there was $142.3 million available for repurchases. Our stock repurchase plan may be suspended or discontinued at any time. The actual timing, number and value of shares repurchased depends on a number of factors, including the market price of our common stock, general market and economic conditions, shares withheld for taxes associated with the vesting of restricted stock and other corporate considerations. The current stock repurchase plan will expire on November 19, 2020.

During the three months ended March 31, 2019, we repurchased an aggregate of 110,054 shares of our common stock at an average cost of $178.72 per share to satisfy tax withholding obligations for certain employees upon the vesting of restricted stock.

Recent Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements

Management has reviewed all the recently issued, but not yet effective, accounting pronouncements, and does not believe any of these pronouncements will have a material impact to the Company.