Parent Company Only Condensed Financial Information - Summary of Condensed Financial Information of Coastal Financial Corporation on Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
ASSETS
Other investments	$ 10,555	$ 8,478
Other assets	4,229	2,673
Total assets	3,144,467	2,635,517
LIABILITIES AND SHAREHOLDERS’ EQUITY
Junior subordinated debentures, net of issuances costs	3,588	3,586
Subordinated debt, net of debt issuance costs	43,999	24,288
Other liabilities	8,912	8,373
Total liabilities and shareholders’ equity	3,144,467	2,635,517
Coastal Financial Corporation
ASSETS
Cash	22,904	24,306
Investment in trust equities	109	109
Investment in subsidiaries	265,741	202,258
Other investments	3,028	2,482
Total loans receivable	0	350
Other assets	(150)	124
Total assets	291,632	229,629
LIABILITIES AND SHAREHOLDERS’ EQUITY
Junior subordinated debentures, net of issuances costs	3,588	3,586
Subordinated debt, net of debt issuance costs	43,999	24,288
Interest and dividends payable	546	290
Other liabilities	5	243
Shareholders' equity	243,494	201,222
Total liabilities and shareholders’ equity	$ 291,632	$ 229,629