Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Total interest income	$ 14,522	$ 14,860	$ 14,718	$ 14,818	$ 15,063	$ 15,388	$ 14,943	$ 14,386	$ 58,918	$ 59,780	$ 54,346
Total interest expense	631	647	639	644	663	706	748	754	2,561	2,871	2,053
Net Interest Income	13,891	14,213	14,079	14,174	14,400	14,682	14,195	13,632	56,357	56,909	52,293
Provision for loan losses	743	652	200	703	376	676	376	326	2,298	1,754	(636)
Other operating income	10,359	11,935	11,864	9,105	10,104	12,407	11,563	10,535	43,263	44,608	20,034
Compensation expense - RML acquisition payments	708	3,250	687	130	1,225	780	587	1,502	4,775	4,094	0
Other operating expense	17,646	17,936	18,682	17,241	17,004	17,423	17,166	16,959	71,505	68,551	46,923
Income Before Provision for Income Taxes	5,153	4,310	6,374	5,205	5,899	8,210	7,629	5,380	21,042	27,118	26,040
Provision for income taxes	1,458	1,027	1,868	1,699	1,673	2,678	2,686	1,747	6,052	8,784	8,173
Net Income	3,695	3,283	4,506	3,506	4,226	5,532	4,943	3,633	14,990	18,334	17,867
Less: Net income attributable to the noncontrolling interest	105	188	156	130	120	197	162	72	579	551	459
Net Income Attributable to Northrim BanCorp, Inc.	$ 3,590	$ 3,095	$ 4,350	$ 3,376	$ 4,106	$ 5,335	$ 4,781	$ 3,561	$ 14,411	$ 17,783	$ 17,408
Earnings per share, basic (in USD per share)	$ 0.52	$ 0.45	$ 0.63	$ 0.49	$ 0.60	$ 0.78	$ 0.70	$ 0.52	$ 2.09	$ 2.59	$ 2.57
Earnings per share, diluted (in USD per share)	$ 0.51	$ 0.44	$ 0.63	$ 0.48	$ 0.59	$ 0.77	$ 0.69	$ 0.51	$ 2.06	$ 2.56	$ 2.54