Segment Information - Schedule of Segment Information (Details) (USD $) In Thousands, 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 Segment	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of Operating Segments									2
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
Interest expense on deposits, borrowings and junior subordinated debentures	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
Total assets	1,449,349				1,215,006				1,449,349	1,215,006
Loans held for sale	43,866				11,301				43,866	11,301
Borrowings	26,304				6,527				26,304	6,527
Community Banking
Segment Reporting Information [Line Items]
Number of Stores	14								14
Total interest income									54,205	46,074
Interest expense on deposits, borrowings and junior subordinated debentures									1,943	2,040
Net Interest Income									52,262	44,034
Provision (benefit) for loan losses									(636)	(635)
Other operating income									17,929	11,659
Other operating expense									47,502	39,866
Income before provision for income taxes									23,325	16,462
Provision for income taxes									6,224	4,773
Net income									17,101	11,689
Less: Net income attributable to the noncontrolling interest									459	87
Net income attributable to Northrim Bancorp									16,642	11,602
Total assets	1,391,862				1,215,006				1,391,862	1,215,006
Loans held for sale	0				11,301				0	11,301
Borrowings	2,164				6,527				2,164	6,527
Home Mortgage Lending
Segment Reporting Information [Line Items]
Total interest income									753	0
Interest expense on deposits, borrowings and junior subordinated debentures									110	0
Net Interest Income									643	0
Provision (benefit) for loan losses									0	0
Other operating income									2,608	1,227
Other operating expense									1,873	0
Income before provision for income taxes									1,378	1,227
Provision for income taxes									612	504
Net income									766	723
Less: Net income attributable to the noncontrolling interest									0	0
Net income attributable to Northrim Bancorp									766	723
Total assets	57,487				0				57,487	0
Loans held for sale	43,866				0				43,866	0
Borrowings	$ 24,140				$ 0				$ 24,140	$ 0