Basis of Presentation and Consolidation (Policies)	9 Months Ended
Basis of Presentation and Consolidation (Policies)	Sep. 30, 2014
Accounting Policies [Abstract]
Stock Conversion	Stock Conversion On August 22, 2013, the Board of Directors of the Company, LLC and the Bank adopted the Plan of Conversion and Reorganization (“Conversion”) to convert the Company from the mutual holding company form of organization to a stock holding company form of organization with a new Maryland-chartered stock corporation, Coastway Bancorp, Inc. (“Corporation”). At December 31, 2013, stock subscriptions received aggregated $43.4 million and were included in liabilities in the accompanying consolidated balance sheets. Conversion costs had been capitalized and reduced the proceeds from the stock sold in the Conversion. At December 31, 2013, conversion costs amounting to $888,000 were included in other assets in the accompanying consolidated balance sheets. On January 14, 2014, the Conversion was completed and Coastway Bancorp, Inc. became the parent holding company for Coastway Community Bank. A total of 4,827,125 shares of Corporation common stock were sold to depositors and to the general public, including those issued to the Corporation’s tax-qualified employee benefit plans, at $10.00 per share through which the Corporation received net offering proceeds of approximately $46.3 million. Also, on January 14, 2014, the Corporation contributed $300,000 in cash and 122,054 shares of common stock to Coastway Cares Charitable Foundation II which together totaled 3.15% of the gross proceeds of the offering totaling $1.5 million which was recorded as a component of non-interest expense during the three months ended March 31, 2014. The total number of shares of common stock outstanding upon completion of the Conversion was 4,949,179 shares. As part of the Conversion, Coastway Bancorp, Inc. established a liquidation account in an amount equal to the net worth of Coastway Bancorp, MHC as of the date of the latest consolidated balance sheet appearing in the final prospectus distributed in connection with the Conversion, or $27.5 million. The liquidation account will be maintained for the benefit of eligible account holders and supplemental eligible account holders who maintain their accounts at Coastway Community Bank after the Conversion. The liquidation account will be reduced annually to the extent that such account holders have reduced their qualifying deposits as of each anniversary date. Subsequent increases will not restore an account holder’s interest in the liquidation account. In the event of a complete liquidation of the Corporation or the Bank, each eligible account holder will be entitled to receive balances for accounts then held. Subsequent to the Conversion, the Corporation may not declare or pay dividends on, and may not repurchase, any of its shares of common stock if the effect thereof would cause stockholders’ equity to be reduced below the liquidation account balance, applicable regulatory capital maintenance requirements, or if such declaration, payment or repurchase would otherwise violate regulatory requirements.
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of the Corporation and its subsidiaries. All significant intercompany transactions have been eliminated. The unaudited consolidated financial statements of the Corporation presented herein have been prepared in accordance with U.S. Generally Accepted Accounting Principles (“GAAP”) for interim financial information and pursuant to the rules of the SEC for quarterly reports on Form 10-Q and Article 8 of Regulation S-X and do not include all of the information and note disclosures required by GAAP for a complete set of financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) and disclosures necessary for the fair presentation of the accompanying consolidated financial statements have been included. Interim results are not necessarily reflective of the results of the entire year. The accompanying unaudited financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2013, included in the Corporation’s annual report on Form 10-K. In preparing the consolidated financial statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of the allowance for loan losses, the valuation of deferred tax assets, and valuation of real estate held for sale.
Recent Accounting Pronouncements	Recent Accounting Pronouncements As an “emerging growth company” as defined in Title 1 of the Jumpstart Our Business Startups (JOBS) Act, the Corporation has elected to use the extended transition period to delay the adoption of new or reissued accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. As of September 30, 2014, there is no significant difference in the comparability of the financial statements as a result of this extended transition period. In February 2013, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2013-02, Reporting of Amounts Reclassified out of Accumulated Other Comprehensive Income. This update requires entities to provide information about the amounts reclassified out of accumulated other comprehensive income by component. In addition, entities are required to present, either on the face of the statement where net income is presented or in the notes, significant amounts reclassified out of accumulated other comprehensive income by the respective line items of net income. This ASU is effective prospectively for public entities for reporting periods beginning after December 15, 2012 and for nonpublic entities for reporting periods beginning after December 15, 2013. Under the extended transition period for an emerging growth company, the Corporation adopted this ASU on January 1, 2014. The impact of adoption of this ASU was not material to the presentation of comprehensive income in the Corporation’s consolidated financial statements. In January 2014, the FASB issued ASU 2014-04, Receivables-Troubled Debt Restructurings by Creditors (Subtopic 310-40) which is intended to reduce diversity by clarifying when an in substance repossession or foreclosure occurs, that is, when a creditor should be considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan such that the loan receivable should be derecognized and the real estate property recognized. The ASU also provides guidance on disclosures of the amount of foreclosed residential real estate properties and of the recorded investment in consumer mortgage loans that are in process of foreclosure. Under the extended transition period for an emerging growth company, the Corporation will adopt this standard for annual periods beginning after December 15, 2014 and interim periods within annual periods beginning after December 15, 2015 and it is not expected to have a material impact.