Parent Company Information - Statements Of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net income	$ 214	$ 5,523	$ 3,589	$ 3,825	$ 3,590	$ 3,095	$ 4,350	$ 3,376	$ 13,151	$ 14,411	$ 17,783
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Stock-based compensation									665	778	608
Net Cash Provided by Operating Activities									19,284	20,123	10,635
Investing Activities:
Purchases of investment securities available for sale									(84,339)	(145,707)	(210,308)
Net Cash Provided (Used) by Investing Activities									30,378	(47,499)	(63,455)
Financing Activities:
Dividends paid to shareholders									(5,965)	(5,372)	(5,117)
Repurchase of common stock									(1,607)	0	0
Net Cash (Used) Provided by Financing Activities									(22,372)	19,254	42,937
Net Change in Cash and Cash Equivalents									27,290	(8,122)	(9,883)
Cash and Cash Equivalents at Beginning of Year				50,551				58,673	50,551	58,673	68,556
Cash and Cash Equivalents at End of Year	77,841				50,551				77,841	50,551	58,673
Northrim Bancorp, Inc.
Operating Activities:
Net income									13,151	14,411	17,783
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Equity in undistributed earnings from subsidiaries									(14,101)	(15,396)	(19,005)
Stock-based compensation									665	778	608
Changes in other assets and liabilities									176	(1,458)	(298)
Net Cash Provided by Operating Activities									(109)	(1,665)	(912)
Investing Activities:
Purchases of investment securities available for sale									(499)	(1,373)	(3,549)
Proceeds from sales/calls/maturities of securities available for sale									0	0	2,998
Investment in Northrim Bank, NISC, NCT1 & NST2									11,989	10,115	9,842
Net Cash Provided (Used) by Investing Activities									11,490	8,742	9,291
Financing Activities:
Dividends paid to shareholders									(5,965)	(5,372)	(5,117)
Proceeds from issuance of common stock and excess tax benefits									100	0	106
Repurchase of common stock									(1,607)	0	0
Net Cash (Used) Provided by Financing Activities									(7,472)	(5,372)	(5,011)
Net Change in Cash and Cash Equivalents									3,909	1,705	3,368
Cash and Cash Equivalents at Beginning of Year				$ 11,963				$ 10,258	11,963	10,258	6,890
Cash and Cash Equivalents at End of Year	$ 15,872				$ 11,963				$ 15,872	$ 11,963	$ 10,258