Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Data [Abstract]
Total interest income	$ 18,062	$ 17,837	$ 17,306	$ 16,878	$ 17,207	$ 16,580	$ 15,595	$ 14,795	$ 70,083	$ 64,177	$ 60,108
Total interest expense	1,652	1,531	1,349	1,109	1,070	761	606	532	5,641	2,969	2,430
Net Interest Income	16,410	16,306	15,957	15,769	16,137	15,819	14,989	14,263	64,442	61,208	57,678
(Benefit) provision for loan losses	(150)	(2,075)	300	750	(200)	0	(300)	0	(1,175)	(500)	3,200
Other operating income	9,735	10,509	9,569	7,533	7,718	8,673	8,314	7,462	37,346	32,167	40,474
Compensation expense - RML acquisition payments	468	0	0	0	0	0	0	0	468	0	130
Other operating expense	20,147	19,324	19,819	17,080	18,300	18,099	16,606	16,795	76,370	69,800	71,023
Income Before Provision for Income Taxes	5,680	9,566	5,407	5,472	5,755	6,393	6,997	4,930	26,125	24,075	23,799
Provision for income taxes	1,100	2,028	1,146	1,160	907	1,129	1,167	868	5,434	4,071	10,321
Net Income					4,848	5,264	5,830	4,062	20,691	20,004	13,478
Less: Net income attributable to the noncontrolling interest					0	0	0	0	0	0	327
Net Income Attributable to Northrim BanCorp, Inc.	$ 4,580	$ 7,538	$ 4,261	$ 4,312	$ 4,848	$ 5,264	$ 5,830	$ 4,062	$ 20,691	$ 20,004	$ 13,151
Earnings per share, basic (in USD per share)	$ 0.70	$ 1.13	$ 0.62	$ 0.63	$ 0.70	$ 0.77	$ 0.85	$ 0.59	$ 3.08	$ 2.91	$ 1.91
Earnings per share, diluted (in USD per share)	$ 0.69	$ 1.11	$ 0.62	$ 0.62	$ 0.69	$ 0.75	$ 0.84	$ 0.58	$ 3.04	$ 2.86	$ 1.88