Segment Information - Schedule of Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) bank	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment bank	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Interest income	$ 15,519	$ 14,860	$ 44,876	$ 44,396
Interest expense	602	647	1,882	1,930
Net Interest Income	14,917	14,213	42,994	42,466
Provision for loan losses	2,500	652	3,200	1,555
Other operating income	13,794	11,935	32,408	32,904
Compensation expense - RML acquisition payments	149	3,250	323	4,067
Other operating expense	17,481	17,936	52,379	53,859
Income Before Provision for Income Taxes	8,581	4,310	19,500	15,889
Provision for income taxes	2,980	1,027	6,236	4,594
Net Income	5,601	3,283	13,264	11,295
Less: Net income attributable to the noncontrolling interest	78	188	327	474	$ 579
Net Income Attributable to Northrim BanCorp, Inc.	5,523	3,095	12,937	10,821	14,411
Total assets	1,523,341		1,523,341		1,526,540
Loans held for sale	$ 59,214		$ 59,214		43,596
Community Banking
Segment Reporting Information [Line Items]
Number of branches | bank	14		14
Interest income	$ 14,953	14,267	$ 43,550	42,962
Interest expense	388	366	1,483	1,299
Net Interest Income	14,565	13,901	42,067	41,663
Provision for loan losses	2,500	652	3,200	1,555
Other operating income	7,575	3,594	14,388	10,357
Compensation expense - RML acquisition payments	149	3,250	323	4,067
Other operating expense	12,191	11,649	37,044	36,459
Income Before Provision for Income Taxes	7,300	1,944	15,888	9,939
Provision for income taxes	2,452	50	4,745	2,140
Net Income	4,848	1,894	11,143	7,799
Less: Net income attributable to the noncontrolling interest	78	188	327	474
Net Income Attributable to Northrim BanCorp, Inc.	4,770	1,706	10,816	7,325
Total assets	1,441,406		1,441,406		1,459,950
Loans held for sale	0		0		0
Home Mortgage Lending
Segment Reporting Information [Line Items]
Interest income	566	593	1,326	1,434
Interest expense	214	281	399	631
Net Interest Income	352	312	927	803
Provision for loan losses	0	0	0	0
Other operating income	6,219	8,341	18,020	22,547
Compensation expense - RML acquisition payments	0	0	0	0
Other operating expense	5,290	6,287	15,335	17,400
Income Before Provision for Income Taxes	1,281	2,366	3,612	5,950
Provision for income taxes	528	977	1,491	2,454
Net Income	753	1,389	2,121	3,496
Less: Net income attributable to the noncontrolling interest	0	0	0	0
Net Income Attributable to Northrim BanCorp, Inc.	753	$ 1,389	2,121	$ 3,496
Total assets	81,935		81,935		66,590
Loans held for sale	$ 59,214		$ 59,214		$ 43,596