Parent Company Information - Statements Of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net income	$ 4,580	$ 7,538	$ 4,261	$ 4,312	$ 4,848	$ 5,264	$ 5,830	$ 4,062	$ 20,691	$ 20,004	$ 13,151
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Change in fair value of marketable equity securities									(911)	625	0
Stock-based compensation									832	816	665
Net Cash (Used) Provided by Operating Activities									(821)	25,150	19,284
Investing Activities:
Purchases of marketable equity securities									(132,104)	(88,139)	(84,339)
Proceeds from sales/calls/maturities of securities available for sale									130,482	122,644	102,660
Net Cash (Used) Provided by Investing Activities									(71,920)	5,646	30,378
Financing Activities:
Dividends paid to shareholders									(8,512)	(7,064)	(5,965)
Repurchase of common stock									(12,569)	(494)	(1,607)
Net Cash Provided (Used) by Financing Activities									90,627	(31,099)	(22,372)
Net Change in Cash and Cash Equivalents									17,886	(303)	27,290
Cash and Cash Equivalents at Beginning of Year				77,538				77,841	77,538	77,841	50,551
Cash and Cash Equivalents at End of Year	95,424				77,538				95,424	77,538	77,841
Northrim Bancorp, Inc.
Operating Activities:
Net income									20,691	20,004	13,151
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Equity in undistributed earnings from subsidiaries									(20,897)	(20,920)	(14,132)
Change in fair value of marketable equity securities									(911)	625	0
Stock-based compensation									832	816	665
Changes in other assets and liabilities									8,556	(6,428)	207
Net Cash (Used) Provided by Operating Activities									8,271	(5,903)	(109)
Investing Activities:
Purchases of marketable equity securities									0	(3,000)	(499)
Proceeds from sales/calls/maturities of securities available for sale									229	783	0
Investment in Northrim Bank, NISC, NCT1 & NST2									19,488	17,877	11,989
Net Cash (Used) Provided by Investing Activities									19,717	15,660	11,490
Financing Activities:
Dividends paid to shareholders									(8,512)	(7,064)	(5,965)
Proceeds from issuance of common stock and excess tax benefits									73	243	100
Repurchase of common stock									(12,569)	(494)	(1,607)
Net Cash Provided (Used) by Financing Activities									(21,008)	(7,315)	(7,472)
Net Change in Cash and Cash Equivalents									6,980	2,442	3,909
Cash and Cash Equivalents at Beginning of Year				$ 18,314				$ 15,872	18,314	15,872	11,963
Cash and Cash Equivalents at End of Year	$ 25,294				$ 18,314				$ 25,294	$ 18,314	$ 15,872