Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) bank	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment bank	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Interest income	$ 15,595	$ 14,892	$ 30,390	$ 29,357
Interest expense	606	648	1,138	1,280
Net Interest Income	14,989	14,244	29,252	28,077
Benefit for loan losses	(300)	300	(300)	700
Other operating income	8,314	9,762	15,776	18,667
Compensation expense - RML acquisition payments	0	0	0	174
Other operating expense	16,606	18,510	33,401	34,951
Income Before Provision for Income Taxes	6,997	5,196	11,927	10,919
Provision for income taxes	1,167	1,455	2,035	3,256
Net Income	5,830	3,741	9,892	7,663
Less: Net income attributable to the noncontrolling interest	0	152	0	249	$ 327
Net Income Attributable to Northrim BanCorp, Inc.	5,830	3,589	9,892	7,414	13,151
Total assets	1,470,440		1,470,440		1,518,596
Loans held for sale	$ 54,306		$ 54,306		43,979
Community Banking
Segment Reporting Information [Line Items]
Number of stores | bank	14		14
Interest income	$ 15,057	14,482	$ 29,520	28,597
Interest expense	443	529	870	1,095
Net Interest Income	14,614	13,953	28,650	27,502
Benefit for loan losses	(300)	300	(300)	700
Other operating income	2,836	3,411	5,354	6,866
Compensation expense - RML acquisition payments				174
Other operating expense	11,748	13,284	24,115	24,906
Income Before Provision for Income Taxes	6,002	3,780	10,189	8,588
Provision for income taxes	882	871	1,541	2,293
Net Income		2,909		6,295
Less: Net income attributable to the noncontrolling interest		152		249
Net Income Attributable to Northrim BanCorp, Inc.	5,120	2,757	8,648	6,046
Total assets	1,392,329		1,392,329		1,452,602
Loans held for sale	0		0		0
Home Mortgage Lending
Segment Reporting Information [Line Items]
Interest income	538	410	870	760
Interest expense	163	119	268	185
Net Interest Income	375	291	602	575
Benefit for loan losses	0	0	0	0
Other operating income	5,478	6,351	10,422	11,801
Compensation expense - RML acquisition payments				0
Other operating expense	4,858	5,226	9,286	10,045
Income Before Provision for Income Taxes	995	1,416	1,738	2,331
Provision for income taxes	285	584	494	963
Net Income		832		1,368
Less: Net income attributable to the noncontrolling interest		0		0
Net Income Attributable to Northrim BanCorp, Inc.	710	$ 832	1,244	$ 1,368
Total assets	78,111		78,111		65,994
Loans held for sale	$ 54,306		$ 54,306		$ 43,979