Description of Business and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2022
Accounting Policies [Abstract]
Description of Business and Summary of Significant Accounting Policies	- Description of Business and Summary of Significant Accounting Policies Nature of operations - Coastal Financial Corporation (“Corporation” or “Company”) is a registered bank holding company whose wholly owned subsidiaries are Coastal Community Bank (“Bank”) and Arlington Olympic LLC (“LLC”). The Company is a Washington state corporation that was organized in 2003. The Bank was incorporated and commenced operations in 1997 and is a Washington state-chartered commercial bank that is a member bank of the Federal Reserve system. Arlington Olympic LLC was formed in 2019 and owns the Company’s Arlington branch site, which the Bank leases from the LLC. We are headquartered in Everett, Washington, which by population is the largest city in, and the county seat of, Snohomish County. The Company’s business is conducted through two reportable segments: the community bank and CCBX. The primary focus of the community bank is on providing a wide range of banking products and services to consumers and small to medium-sized businesses, professionals, and individuals in the broader Puget Sound region in the state of Washington through its 14 branches in Snohomish, Island and King Counties, and through the Internet and its mobile banking application. The CCBX segment provides Banking as a Service (“BaaS”) that allows our broker dealers and digital financial service partners to offer their customers banking services. Through CCBX’s partners the Company is able to offer banking services and products across the nation. The Bank’s deposits are insured in whole or in part by the Federal Deposit Insurance Corporation (“FDIC”). The community bank’s loans and deposits are primarily within the greater Puget Sound area, while CCBX loans and deposits are dependent upon the partner’s market. The Bank’s primary funding source is deposits from customers. The Bank is subject to regulation and supervision by the Board of Governors of the Federal Reserve System (the “Federal Reserve”) and the Washington State Department of Financial Institutions Division of Banks. The Federal Reserve also has regulatory and supervisory authority over the Company. Financial statement presentation - The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim reporting requirements and with instructions to Form 10-Q and Article 10 of Regulation S-X, and therefore do not include all the information and notes included in the annual consolidated financial statements in conformity with GAAP. These interim condensed consolidated financial statements and accompanying notes should be read in conjunction with the Company’s audited consolidated financial statements and accompanying notes included in the Company’s Annual report on Form 10-K as filed with the U.S. Securities and Exchange Commission (“SEC”) on March 14, 2022. Operating results for the three months and nine months ended September 30, 2022 are not necessarily indicative of the results that may be expected for the entire year. Amounts presented in the consolidated financial statements and footnote tables are rounded and presented in thousands of dollars except per-share amounts, which are presented in dollars. In the narrative footnote discussion, amounts are rounded to thousands and presented in dollars. In management’s opinion, all accounting adjustments necessary to accurately reflect the financial position and results of operations on the accompanying consolidated financial statements have been made. These adjustments include normal and recurring accruals considered necessary for a fair and accurate presentation. Principles of consolidation - The consolidated financial statements include the accounts of the Company, the Bank and the LLC. All significant intercompany accounts have been eliminated in consolidation. Estimates - The preparation of financial statements in conformity with 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 date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management believes that its critical accounting policies include determining the allowance for loan losses, the valuation of the Company’s deferred tax assets, and fair value of financial instruments. Actual results could differ significantly from those estimates. Accounting policy update– During the nine months ended September 30, 2022, the Company transferred $128.2 million in CCBX loans receivable to loans held for sale. These CCBX loans held for sale consist of the portion of CCBX partner loans that the Company intends to sell back to the originating CCBX partner at par. As of September 30, 2022 there were $43.3 million in CCBX partner loans held for sale recorded at par, compared to zero at December 31, 2021. Community bank loans held-for-sale consist of the guaranteed portion of SBA loans and United States Department of Agriculture (“USDA”) loans the Company intends to sell after origination and are reflected at the lower of aggregate cost or fair value. Loans are generally sold with servicing of the sold portion retained by the Company when the sale of the loan occurs, the premium received is combined with the estimated present value of future cash flows on the related servicing asset and recorded as a gain on sale of loans in noninterest income. There were no community bank loans held for sale at September 30, 2022 or December 31, 2021. Subsequent Events - The Company has evaluated events and transactions subsequent to September 30, 2022 for potential recognition or disclosure. On November 1, 2022 the Company completed its private placement of $20.0 million in fixed-to-floating rate subordinated notes due November 1, 2032 (the “Notes”). The Notes will bear interest at a fixed annual rate of 7.00% for the first five years and will reset quarterly thereafter to the then-current three-month Secured Overnight Financing Rate ("SOFR") plus 290 basis points. The Company intends to use the net proceeds from the offering for general corporate purposes. The Company is entitled to redeem the Notes, in whole or in part, on any interest payment date on or after November 1, 2027, or at any time, in whole but not in part, upon certain other specified events prior to the Notes’ maturity on November 1, 2032. Reclassifications - Certain amounts reported in prior quarters' consolidated financial statements may have been reclassified to conform to the current presentation with no effect on stockholders’ equity or net income.