Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2023
Accounting Policies [Abstract]
Organization of the Company and Basis of Presentation	Organization of the Company and Basis of Presentation The accompanying unaudited consolidated interim financial statements and these notes should be read in conjunction with the December 31, 2022 audited consolidated financial statements and notes thereto contained in the Annual Report on Form 10-K of Enterprise Bancorp, Inc. (the "Company," "Enterprise," "we," or "our") for the year ended December 31, 2022 (the "2022 Annual Report on Form 10-K") as filed with the Securities and Exchange Commission (the "SEC") on March 8, 2023. The Company has not materially changed its significant accounting policies from those disclosed in its 2022 Annual Report on Form 10-K. See Item (d), "Recent Accounting Pronouncements," below in this Note 1. The accompanying unaudited consolidated interim financial statements of the Company include the accounts of the Company and its wholly owned subsidiary, Enterprise Bank and Trust Company, commonly referred to as Enterprise Bank (the "Bank"). The Bank is a Massachusetts trust company and state chartered commercial bank organized in 1989. Substantially all of the Company's operations are conducted through the Bank and its subsidiaries. The Bank's subsidiaries include Enterprise Insurance Services, LLC and Enterprise Wealth Services, LLC, both organized under the laws of the State of Delaware, to engage in insurance sales activities and offer non-deposit investment products and services, respectively. In addition, the Bank has the following subsidiaries that are incorporated in the Commonwealth of Massachusetts and classified as security corporations in accordance with applicable Massachusetts General Laws: Enterprise Security Corporation; Enterprise Security Corporation II; and Enterprise Security Corporation III. The security corporations, which hold various types of qualifying securities, are limited to conducting investment activities that the Bank itself would be allowed to conduct under applicable laws. In February 2023, the Bank organized the EBTC NMTC Investment Fund - CHC, LLC (the "NMTC Investment Fund") under the laws of the State of Delaware, in conjunction with the Banks investment in a qualifying New Market Tax Credit ("NMTC") project. The NMTC Investment Fund is the Company's only unconsolidated Variable Interest Entity ("VIE"). The services offered through the Bank and its subsidiaries are managed as one strategic unit and represent the Company's only reportable operating segment.
Organization of the Company and Basis of Presentation - Basis of Accounting	The accompanying unaudited consolidated interim financial statements, and notes thereto, in this Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2023 (this "Form 10-Q"), have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial information and the SEC instructions for Quarterly Reports on Form 10-Q. In the opinion of management, the accompanying unaudited consolidated interim financial statements reflect all necessary adjustments, consisting of normal recurring accruals and elimination of intercompany balances, for a fair presentation.
Organization of the Company and Basis of Presentation - Reclassifications	Interim results are not necessarily indicative of results to be expected for the entire year, or any future period.
Uses of Estimates	Uses of Estimates In preparing the unaudited consolidated interim financial statements in conformity with GAAP, management is required to exercise judgment in determining many of the methodologies, assumptions and estimates to be utilized. These assumptions and estimates affect the reported values of assets and liabilities as of the balance sheet dates and income and expenses for the period then ended. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates should the assumptions and estimates used be incorrect or change over time due to changes in circumstances. Changes in those estimates resulting from continuing changes in the economic environment and other factors will be reflected in the consolidated financial statements and results of operations in future periods. As discussed in the Company's 2022 Annual Report on Form 10-K, the most significant areas in which management applies critical assumptions and estimates are: the estimates of the allowance for credit losses ("ACL") for loans, available for sale securities and reserve for unfunded commitments, and the impairment review of goodwill. Refer to Note 1, "Summary of Significant Accounting Policies," to the Company's audited consolidated financial statements included in the Company's 2022 Annual Report on Form 10-K for accounting policies related to these significant estimates.
Unconsolidated Variable Interest Entity / Proportional Accounting	Unconsolidated Variable Interest Entity / Proportional Accounting In March 2023, the Bank made an equity contribution to the NMTC Investment Fund a newly formed Limited Liability Company in order to invest in NMTC, a program, which is administered by the U.S. Department of the Treasury's Community Development Financial Institutions Fund and allocated to Community Development Entities ("CDE"). The NMTC program provides federal tax incentives for investments in distressed communities and promotes economic improvements through the development of successful businesses in these communities. The NMTCs are available to investors over a seven-year period and are subject to recapture if certain events occur during such period. The Bank invested $3.7 million in the Investment Fund and anticipates receiving $4.8 million of federal tax credits over the next seven years (5% in each of the first three years, and 6% in each of the next four years). The underlying project is structured through a qualified CDE, which in turn has made loans to a qualified active low-income business. The Bank has no unfunded commitments associated with its NMTC investment. The Company has elected to account for the tax equity investment, using the proportional amortization method. Under this method the NMTC Investment Fund is not consolidated with the Company and instead, the initial cost of the investment is amortized in proportion to the amount of tax credits and other tax benefits received over the allotment period. The investment is carried within the line "Prepaid expenses and other assets" on the Company's Consolidated Balance Sheet and the investment amortization expense and tax credits are presented on a net basis within the line "Provision for income taxes" on the Company's Consolidated Statements of Income. During the three months ended March 31, 2023, the related amortization expense and tax credits amounted to $44 thousand and $153 thousand, respectively.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Accounting pronouncements adopted by the Company In March 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2023-02, "Investments—Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method." ASU 2023-02 permits reporting entities to elect to account for their tax equity investments, regardless of the tax credit program from which the income tax credits are received, using the proportional amortization method if certain conditions are met. The election can be made for each individual qualifying tax credit investment. Under the proportional amortization method, the initial cost of an investment is amortized in proportion to the amount of tax credits and other tax benefits received, with the amortization and tax credits recognized as a component of income tax expense. To qualify for the proportional amortization method, all of the following conditions must be met: (1) It is probable that the income tax credits allocated to the tax equity investor will be available; (2) The tax equity investor does not have the ability to exercise significant influence over the operating and financial policies of the underlying project; (3) Substantially all of the projected benefits are from income tax credits and other income tax benefits; (4) The tax equity investor's projected yield based solely on the cash flows from the income tax credits and other income tax benefits is positive; and (5) The tax equity investor is a limited liability investor in the limited liability entity for both legal and tax purposes, and the tax equity investor's liability is limited to its capital investment. Under the proportional amortization method, the investment shall be tested for impairment when events or changes in circumstances indicate that it is more likely than not that the carrying amount of the investment will not be realized. An impairment loss shall be measured as the amount by which the carrying amount of an investment exceeds its fair value. A previously recognized impairment loss shall not be reversed. ASU 2023-02 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2023. The Company has elected to early adopt ASU 2022-01 effective on January 1, 2023, applying the new guidance to a new investment in NMTC made in the first quarter of 2023, and the adoption did not have a significant impact on the financial statements. In March 2022, the FASB issued ASU 2022-01, "Derivatives and Hedging (Topic 815): Fair Value Hedging—Portfolio Layer Method." This ASU clarifies the guidance on fair value hedge accounting of interest rate risk for portfolios of financial assets. The ASU amends the guidance in ASU 2017-12, "Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities," that, among other things, established the "last-of-layer" method for making the fair value hedge accounting for these portfolios more accessible. ASU 2022-01 renames that method the "portfolio layer" method and addresses feedback from stakeholders regarding its application. The Company adopted ASU 2022-01 effective on January 1, 2023 and the adoption did not have a significant impact on the financial statements. In March 2022, the FASB issued ASU 2022-02, "Financial Instruments—Credit Losses (Topic 326), Troubled Debt Restructurings and Vintage Disclosures." This ASU eliminates the accounting guidance for troubled debt restructurings by creditors that have adopted the current expected credit loss ("CECL") methodology for estimating allowances for credit losses and enhances the disclosure requirements for loan restructurings made with borrowers experiencing financial difficulty. In addition, the amendments require a public business entity to disclose current-period gross charge-offs for financing receivables and net investment in leases by year of origination in the vintage disclosures. The Company adopted ASU 2022-02 effective on January 1, 2023, prospectively, and the adoption did not have a significant impact on the financial statements.
Subsequent Events	Subsequent Events The Company has evaluated subsequent events and transactions from March 31, 2023 through the date this Form 10-Q was filed with the SEC for potential recognition or disclosure as required by GAAP and determined there were no material subsequent events requiring recognition or disclosure.