Basis of Presentation and Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Description of Business and Operations — Bentley Systems, Incorporated (“Bentley” or the “Company”) is a Delaware corporation that was founded in 1984 and is headquartered in Exton, Pennsylvania. The Company, together with its subsidiaries, is a leading global provider of infrastructure engineering software solutions for professionals and organizations involved in the project delivery and operational performance of infrastructure assets. The Company is dedicated to advancing infrastructure through its comprehensive software solutions that span engineering disciplines, assets, and lifecycle processes. The Company’s integrated software platform encompasses both the design and construction of infrastructure, which the Company refers to as project delivery, and the operation of infrastructure assets, which the Company refers to as asset performance. The Company’s software solutions are designed to enable information mobility for a more complete flow of information among applications, across distributed project teams, from offices to the field, and throughout the infrastructure lifecycle. The Company believes its solutions extend the reach and scope of digital engineering models from the project delivery phase into the asset performance phase of the infrastructure lifecycle, which enables engineers to make infrastructure assets more intelligent and sustainable. Users of the Company’s solutions include engineers and construction professionals who collaborate on project delivery, and owner‑operators who maintain, adapt, and optimize the performance of infrastructure assets. Initial Public Offering — On September 25, 2020, the Company completed its initial public offering (“IPO”). The selling stockholders identified in the Company’s registration statement on Form S-1, as amended, on file with the U.S. Securities and Exchange Commission (“SEC”) sold 12,360,991 shares of Class B Common Stock at a public offering price of $22.00 per share. The Company did not sell any shares in the IPO and did not receive any of the proceeds from the sale of the Class B Common Stock sold by the selling stockholders (see Notes 13 and 15). For the three and nine months ended September 30, 2020, the Company recorded $26,130 in Expenses associated with initial public offering in the consolidated statements of operations. Expenses associated with initial public offering include certain non‑recurring costs relating to the Company’s IPO, consisting of the payment of underwriting discounts and commissions applicable to the sale of shares by the selling stockholders, professional fees, and other expenses. Special Dividend — On August 28, 2020, the Company’s board of directors declared a special dividend of $1.50 per share of the Company’s common stock ($392,489 in the aggregate) (the “Special Dividend”), payable to all stockholders of record as of August 31, 2020, including dividends which accrue on certain unvested restricted stock and restricted stock units (“RSUs”). The Company used its bank credit facility to pay the Special Dividend (see Note 10). In connection with the Special Dividend declaration, an in kind adjustment was made to phantom shares issuable pursuant to the amended and restated Bentley Systems, Incorporated Nonqualified Deferred Compensation Plan (the “DCP”) (see Note 12) and the exercise price of all outstanding stock options at that time were reduced by $1.50, but not lower than $0.01 (see Note 15). Risks and Uncertainties — COVID‑19 Pandemic — In March 2020, the World Health Organization declared a global pandemic related to the rapidly growing outbreak of the disease COVID‑19, caused by a novel strain of coronavirus, SARS‑CoV‑2. The COVID‑19 outbreak and certain preventative or protective actions that governments, businesses, and individuals have taken in respect of COVID‑19 have resulted in global business disruptions. In response to the COVID‑19 pandemic, the Company implemented a number of initiatives to ensure the safety of its colleagues and enable them to move to a work from home environment seamlessly and continue working effectively. The Company’s business model is such that there was minimal disruption to the Company’s ability to deliver its solutions to accounts, and the Company believes it did not have any loss of productivity during this transition. The Company has also taken measures to reduce selected operating expenses, including various costs associated with travel and facilities. Much of those resulting savings have been or will be re-invested in a portfolio of businesses outside of the Company’s core software business. Basis of Presentation and Consolidation — The unaudited consolidated financial statements and accompanying notes have been prepared in United States (“U.S.”) Dollars and in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information along with the instructions to Form 10‑Q and Article 10 of SEC Regulation S‑X. Accordingly, they do not include all of the information and notes required by U.S. GAAP for annual financial statements. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments, consisting only of those of a normal recurring nature, necessary for a fair statement of the Company’s financial position, results of operations, and cash flows at the dates and for the periods indicated. The December 31, 2019 consolidated balance sheet included herein is derived from the Company’s audited consolidated financial statements included in the Company’s registration statement on Form S‑1, as amended, on file with the SEC. The results of operations for the nine months ended September 30, 2020 are not necessarily indicative of the results expected for the remainder of the fiscal year. The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. The Company is party to a joint venture and an investment, both of which are accounted for using the equity method. All significant intercompany accounts and transactions have been eliminated in consolidation. The Company’s principal subsidiaries are Bentley Systems International Limited (Ireland), Bentley Software International, Limited (Bermuda), Bentley Canada Inc. (Canada), Bentley Systems Europe BV (the Netherlands), Bentley Systems Pty Ltd. (Australia), Bentley Systems Co., Ltd. (Japan), Bentley Systems Germany GmbH (Germany), Bentley Systems Ltd. (UK), and Bentley Systems India Private Limited (India). Use of Estimates — The preparation of consolidated financial statements and related disclosures in conformity with U.S. 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 dates of the financial statements and the reported amounts of revenues and expenses during the reporting periods. The Company’s significant estimates and assumptions include revenue recognition, adequacy of allowance for accounts receivable, determination of the fair value of acquired assets and liabilities, the fair value of derivative financial instruments, the fair value of common stock and stock‑based compensation, operating lease assets and liabilities, useful lives for depreciation and amortization, impairment of goodwill and intangible assets, and accounting for income taxes. Actual results could differ materially from these estimates. Derivatives Not Designated As Hedging Instruments — On March 31, 2020, the Company entered into an interest rate swap with a notional amount of $200,000 and a ten‑year term to reduce the interest rate risk associated with the Company’s Credit Facility (see Note 10). The interest rate swap is not designated as a hedging instrument for accounting purposes. The Company accounts for the swap as either an asset or a liability on the consolidated balance sheet and carries the derivative at fair value. Gains and losses from the change in fair value are recognized in Other income (expense), net and payments related to the swap are recognized in Interest expense, net in the consolidated statements of operations. The bank counterparty to the derivative potentially exposes the Company to credit-related losses in the event of nonperformance. To mitigate that risk, the Company only contracts with counterparties who meet the Company’s minimum requirements under its counterparty risk assessment process. The Company monitors counterparty risk on at least a quarterly basis and adjusts its exposure as necessary. The Company does not enter into derivative instrument transactions for trading or speculative purposes. Leases — The Company determines if an arrangement is a lease at inception. Operating leases are included in Operating lease right‑of‑use assets, Operating lease liabilities, and Long‑term operating lease liabilities in the Company’s consolidated balance sheet. Operating lease right‑of‑use assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease right‑of‑use assets and operating lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate, if the Company’s leases do not provide an implicit rate, based on the information available at the commencement date in determining the present value of lease payments. The incremental borrowing rate is determined based on the Company’s estimated credit rating, the term of the lease, economic environment where the asset resides, and full collateralization. The operating lease right‑of‑use assets also include any lease payments made and are reduced by any lease incentives. Options to extend or terminate the lease are considered in determining the lease term when it is reasonably certain that the option will be exercised. Lease expense for lease payments is recognized on a straight‑line basis over the lease term. The Company’s operating leases are primarily for office space, cars, and office equipment. The Company’s finance lease is included in Property and equipment, net, Accruals and other current liabilities, and Other liabilities in the Company’s consolidated balance sheet. Significant Accounting Policies — There have been no changes other than what is discussed herein to the Company’s significant accounting policies as compared to the significant accounting policies described in Note 1 to the Company’s consolidated financial statements as of and for the year ended December 31, 2019 included in the Company’s registration statement on Form S‑1, as amended, on file with the SEC. These unaudited consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes as of and for the year ended December 31, 2019 included in the Company’s registration statement on Form S‑1, as amended, on file with the SEC.