Consolidated Financial Statements	6 Months Ended
Consolidated Financial Statements	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidated Financial Statements	Consolidated Financial Statements Basis of Presentation The consolidated financial statements are comprised of the accounts of Northfield Bancorp, Inc. (the “Company”) and its wholly owned subsidiaries, Northfield Investments, Inc. and Northfield Bank (the “Bank”), and the Bank’s wholly-owned subsidiaries, NSB Services Corp. and NSB Realty Trust, collectively (the “Company”). All significant intercompany accounts and transactions have been eliminated in consolidation. In the opinion of management, all adjustments (consisting solely of normal and recurring adjustments) necessary for the fair presentation of the consolidated balance sheets and the consolidated statements of comprehensive income for the unaudited periods presented have been included. The results of operations and other data presented for the three and six months ended June 30, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020 or for any other period. Whenever necessary, certain prior year amounts are reclassified to conform to the current year presentation. In preparing the unaudited consolidated financial statements in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”), management has made estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the consolidated balance sheets and the consolidated statements of comprehensive income for the periods indicated. Material estimates that are particularly susceptible to change are: the allowance for loan losses, estimated cash flows of our purchased credit-impaired (“PCI”) loans and the valuation allowance against deferred tax assets. Estimates and assumptions are reviewed periodically and the effects of revisions are reflected in the consolidated financial statements in the period they are deemed necessary. While management uses its best judgment, actual amounts or results could differ significantly from those estimates. Certain information and note disclosures usually included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for the preparation of interim financial statements. The consolidated financial statements presented should be read in conjunction with the audited consolidated financial statements and notes to consolidated financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019, as filed with the SEC. COVID-19 On March 13, 2020, the Coronavirus Disease (COVID-19) pandemic was declared a national emergency by the President of the United States. The spread of COVID-19 has negatively impacted the national and local economy, disrupted supply chains and increased unemployment levels. The resulting temporary closure of many businesses and the implementation of social distancing and stay-at-home policies has and will continue to impact many of the Company’s customers. The Company is committed to supporting its customers, employees and communities during this difficult time and has adapted to the changing environment. The Company has implemented temporary relief assistance to customers, including the consideration of various loan payment deferral and fee waiver options. Branch facilities remained open, but lobbies were temporarily closed for much of the second quarter of 2020, with transactions being conducted through drive-up windows or on-line channels. As of July 6, 2020, bank branches were fully open with additional health, social distancing, and limited capacity measures put in place to meet safety requirements. We have also transitioned the majority of our workforce to work remotely. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security (“CARES”) Act was signed into law. It contains substantial tax and spending provisions intended to address the impact of the COVID-19 pandemic. The CARES Act includes a range of other provisions designed to support the U.S. economy and mitigate the impact of COVID-19 on financial institutions and their customers, including through the authorization of various relief programs and measures that the U.S. Department of the Treasury, the Small Business Administration, the Federal Reserve Board (“FRB”) and other federal banking agencies have implemented or may implement. Under the CARES Act, financial institutions are permitted to delay the adoption of the Financial Accounting Standards Board's (“FASB”) Accounting Standard Update (“ASU”) No. 2016-13, Financial Instruments - Credit Losses (Topic 326) (“CECL”) until the earlier of the termination date of the national emergency declaration or December 31, 2020. The Company has elected to defer the adoption of CECL, with an effective retrospective implementation date of January 1, 2020. The CARES Act also includes a provision that permits a financial institution to elect to suspend temporarily troubled debt restructuring (“TDR”) accounting under ASC Subtopic 310-40. To be eligible, a loan modification must be: (1) related to COVID-19; (2) executed on a loan that was not more than 30 days past due as of December 31, 2019; and (3) executed between March 1, 2020, and the earlier of (a) 60 days after the date of termination of the national emergency or (b) December 31, 2020. This includes short-term (e.g., up to six months) modifications such as payment deferrals, fee waivers, extensions of repayment terms, or delays in payment that are insignificant. Borrowers considered current are those that are less than 30 days past due on their contractual payments at the time a modification program is implemented. The banking regulators issued similar guidance, which also clarified that a COVID-19-related modification should not be considered a TDR if the borrower was current on payments at the time the underlying loan modification program was implemented and if the modification is considered to be short-term. The Company implemented a short-term loan modification program in late March 2020 to provide temporary payment relief to borrowers impacted by COVID-19. The program allows for a deferral of payments typically for 90 days, which may be extended for an additional 90 days, for a maximum of 180 days on a cumulative basis. See Note 5 - Loans for additional details of the Company's loan modification program. A provision in the CARES Act includes a $349 billion fund for the creation of the Paycheck Protection Program (“PPP”) through the Small Business Administration (“SBA”) and Treasury Department. On April 24, 2020, the Paycheck Protection Program and Health Care Enhancement Act was signed into law, adding an additional $310 billion of funding to the PPP. The PPP provides 100% federally guaranteed loans for small businesses to cover payroll, utilities, rent and interest. These small business loans may be forgiven if borrowers maintain their payrolls and satisfy certain other conditions for a period of time during the COVID-19 pandemic. As of June 30, 2020, the Company had funded over 900 PPP loans to new and existing customers, totaling approximately $109.2 million, and benefiting small businesses with over 13,000 employees. PPP provides for lender processing fees that range from 1% to 5% of the final disbursement made to individual borrowers. Based on the Company’s approved disbursements as of June 30, 2020, we estimate our loan processing fees would be approximately $4.0 million which will be recognized in income in future periods over the life of the loans. PPP loans are fully guaranteed by the SBA, unless the lender violated an obligation under the agreement, and are therefore excluded from the allowance for loan and lease losses calculation. The Company continues to maintain a strong liquidity and capital position, despite the economic uncertainties presented by the COVID-19 pandemic. As of June 30, 2020, both the Company and the Bank's capital ratios were in excess of regulatory requirements and are currently classified as well capitalized. The Company maintains access to multiple sources of liquidity and expects to have sufficient funds available to meet current commitments in the normal course of business. While, the Company has not incurred any significant disruption to its business activities as a result of COVID-19, the full impact of the pandemic is unknown and rapidly evolving. The outbreak is having a significant adverse impact on certain industries the Company serves, including retail, accommodations, and restaurants and food services. While most states have re-opened, it is under limited capacities and under other social-distancing restrictions, which has resulted in lower commercial activity and consumer spending. This decrease in commercial activity may result in our customers' inability to meet their loan obligations to us. In addition, the economic pressures and uncertainties related to the COVID-19 pandemic have resulted in changes in consumer spending behaviors, which may negatively impact the demand for loans and other services we offer. Because of the significant uncertainties related to the ultimate duration of the COVID-19 pandemic and its effects on our customers and prospects, and on the local and national economy, there can be no assurances as to how the crisis may ultimately affect the Company's loan portfolio, and business as a whole. The extent of such impact will depend on future developments, which are highly uncertain, including when the coronavirus can be controlled and abated and when and how the economy may be fully reopened. As such, the Company could be subject to certain risks, any of which could have a material, adverse effect on our business, financial condition, liquidity, and results of operations.