Basis of Presentation	9 Months Ended
Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	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 significant subsidiaries, NSB Services Corp. and NSB Realty Trust. 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 financial condition and the consolidated results of operations for the unaudited periods presented have been included. The results of operations and other data presented for the three and nine months ended September 30, 2018, are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2018 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 statements of financial condition and results of operations for the periods indicated. Material estimates that are particularly susceptible to change are: the allowance for loan losses, the evaluation of goodwill and other intangible assets, impairment on investment securities, fair value measurements of assets and liabilities, and income taxes. 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 Annual Report on Form 10-K for the year ended December 31, 2017, of the Company as filed with the SEC.

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 significant subsidiaries, NSB Services Corp. and NSB Realty Trust. 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 financial condition and the consolidated results of operations for the unaudited periods presented have been included. The results of operations and other data presented for the three and nine months ended September 30, 2018, are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2018 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 statements of financial condition and results of operations for the periods indicated. Material estimates that are particularly susceptible to change are: the allowance for loan losses, the evaluation of goodwill and other intangible assets, impairment on investment securities, fair value measurements of assets and liabilities, and income taxes. 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 Annual Report on Form 10-K for the year ended December 31, 2017, of the Company as filed with the SEC.