Quarterly Results of Operations (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Total interest income	$ 15,178	$ 14,212	$ 13,895	$ 11,673	$ 12,018	$ 11,524	$ 11,440	$ 11,092	$ 54,958	$ 46,074	$ 44,728
Total interest expense	642	487	484	440	497	502	511	530	2,053	2,040	2,505
Net interest income	14,536	13,725	13,411	11,233	11,521	11,022	10,929	10,562	52,905	44,034	42,223
Provision (benefit) for loan losses	500	0	(1,136)	0	0	(785)	0	150	(636)	(635)	(1,559)
Other operating income	8,764	4,934	4,106	2,734	2,802	3,243	3,702	3,139	20,537	12,886	15,432
Other operating expense	14,005	13,110	11,950	10,309	10,702	10,076	9,391	9,697	49,375	39,866	39,600
Income Before Provision for Income Taxes	8,795	5,549	6,703	3,658	3,621	4,974	5,240	3,854	24,703	17,689	19,614
Provision for income taxes	1,991	1,651	2,239	955	1,042	1,510	1,635	1,090	6,836	5,277	6,156
Net income	6,804	3,898	4,464	2,703	2,579	3,464	3,605	2,764	17,867	12,412	13,458
Less: Net income attributable to the noncontrolling interest	130	191	95	45	(102)	(10)	109	90	459	87	512
Net income attributable to Northrim Bancorp	$ 6,674	$ 3,707	$ 4,369	$ 2,658	$ 2,681	$ 3,474	$ 3,496	$ 2,674	$ 17,408	$ 12,325	$ 12,946
Earnings per share, basic (USD per share)	$ 0.98	$ 0.54	$ 0.64	$ 0.41	$ 0.41	$ 0.53	$ 0.54	$ 0.41	$ 2.57	$ 1.89	$ 2.00
Earnings per share, diluted (USD per share)	$ 0.97	$ 0.53	$ 0.63	$ 0.40	$ 0.40	$ 0.53	$ 0.53	$ 0.41	$ 2.54	$ 1.87	$ 1.97