Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Total interest income	$ 17,207	$ 16,580	$ 15,595	$ 14,795	$ 15,232	$ 15,519	$ 14,892	$ 14,465	$ 64,177	$ 60,108	$ 58,918
Total interest expense	1,070	761	606	532	548	602	648	632	2,969	2,430	2,561
Net Interest Income	16,137	15,819	14,989	14,263	14,684	14,917	14,244	13,833	61,208	57,678	56,357
Benefit for loan losses	(200)	0	(300)	0	0	2,500	300	400	(500)	3,200	2,298
Other operating income	7,718	8,673	8,314	7,462	7,952	13,855	9,762	8,905	32,167	40,474	43,263
Compensation expense - RML acquisition payments					(193)	149	0	174	0	130	4,775
Other operating expense	18,300	18,099	16,606	16,795	18,530	17,542	18,510	16,441	69,800	71,023	71,505
Income Before Provision for Income Taxes	5,755	6,393	6,997	4,930	4,299	8,581	5,196	5,723	24,075	23,799	21,042
Provision for income taxes	907	1,129	1,167	868	4,085	2,980	1,455	1,801	4,071	10,321	6,052
Net Income					214	5,601	3,741	3,922	20,004	13,478	14,990
Less: Net income attributable to the noncontrolling interest					0	78	152	97	0	327	579
Net Income Attributable to Northrim BanCorp, Inc.	$ 4,848	$ 5,264	$ 5,830	$ 4,062	$ 214	$ 5,523	$ 3,589	$ 3,825	$ 20,004	$ 13,151	$ 14,411
Earnings per share, basic (in USD per share)	$ 0.70	$ 0.77	$ 0.85	$ 0.59	$ 0.03	$ 0.80	$ 0.52	$ 0.55	$ 2.91	$ 1.91	$ 2.09
Earnings per share, diluted (in USD per share)	$ 0.69	$ 0.75	$ 0.84	$ 0.58	$ 0.03	$ 0.79	$ 0.51	$ 0.55	$ 2.86	$ 1.88	$ 2.06