Segment Information - Schedule of Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) bank	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Segment bank	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of segments | Segment			2
Total interest income	$ 15,388	$ 14,212	$ 44,717	$ 39,780
Interest expense on deposits, borrowings and junior subordinated debentures	706	487	2,208	1,411
Net Interest Income	14,682	13,725	42,509	38,369
Provision (benefit) for loan losses	676	0	1,378	(1,136)
Other operating income	12,407	4,934	34,505	11,774
Other operating expense	18,203	12,779	54,418	34,368
Income before provision for income taxes	8,210	5,880	21,218	16,911
Provision for income taxes	2,678	1,982	7,111	5,848
Net income	5,532	3,898	14,107	11,063
Less: Net income attributable to the noncontrolling interest	197	191	431	329	$ 459
Net income attributable to Northrim BanCorp, Inc.	5,335	3,707	13,676	10,734	17,408
Total assets	1,539,253		1,539,253		1,449,349
Loans held for sale	66,597		66,597		43,866
Borrowings	$ 12,458		$ 12,458		26,304
Community Banking
Segment Reporting Information [Line Items]
Number of Stores | bank	14		14
Total interest income	$ 14,883	14,212	$ 43,227	39,780
Interest expense on deposits, borrowings and junior subordinated debentures	458	487	1,302	1,411
Net Interest Income	14,425	13,725	41,925	38,369
Provision (benefit) for loan losses	676	0	1,378	(1,136)
Other operating income	4,294	4,550	11,270	11,166
Other operating expense	12,633	12,779	37,975	34,368
Income before provision for income taxes	5,410	5,496	13,842	16,303
Provision for income taxes	1,523	1,824	4,066	5,598
Net income	3,887	3,672	9,776	10,705
Less: Net income attributable to the noncontrolling interest	197	191	431	329
Net income attributable to Northrim BanCorp, Inc.	3,690	3,481	9,345	10,376
Total assets	1,456,032		1,456,032		1,391,862
Loans held for sale	0		0		0
Borrowings	2,131		2,131		2,164
Home Mortgage Lending
Segment Reporting Information [Line Items]
Total interest income	505	0	1,490	0
Interest expense on deposits, borrowings and junior subordinated debentures	248	0	906	0
Net Interest Income	257	0	584	0
Provision (benefit) for loan losses	0	0	0	0
Other operating income	8,113	384	23,235	608
Other operating expense	5,570	0	16,443	0
Income before provision for income taxes	2,800	384	7,376	608
Provision for income taxes	1,155	158	3,045	250
Net income	1,645	226	4,331	358
Less: Net income attributable to the noncontrolling interest	0	0	0	0
Net income attributable to Northrim BanCorp, Inc.	1,645	$ 226	4,331	$ 358
Total assets	83,221		83,221		57,487
Loans held for sale	66,597		66,597		43,866
Borrowings	$ 10,327		$ 10,327		$ 24,140