Segment Information - Schedule of Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total interest income	$ 18,062	$ 17,837	$ 17,306	$ 16,878	$ 17,207	$ 16,580	$ 15,595	$ 14,795	$ 70,083	$ 64,177	$ 60,108
Interest expense	1,652	1,531	1,349	1,109	1,070	761	606	532	5,641	2,969	2,430
Net Interest Income	16,410	16,306	15,957	15,769	16,137	15,819	14,989	14,263	64,442	61,208	57,678
Provision (benefit) for loan losses	(150)	(2,075)	300	750	(200)	0	(300)	0	(1,175)	(500)	3,200
Total Other Operating Income	9,735	10,509	9,569	7,533	7,718	8,673	8,314	7,462	37,346	32,167	40,474
Compensation expense - RML acquisition payments	468	0	0	0	0	0	0	0	468	0	130
Other operating expense	20,147	19,324	19,819	17,080	18,300	18,099	16,606	16,795	76,370	69,800	71,023
Income Before Provision for Income Taxes	5,680	9,566	5,407	5,472	5,755	6,393	6,997	4,930	26,125	24,075	23,799
Provision for income taxes	1,100	2,028	1,146	1,160	907	1,129	1,167	868	5,434	4,071	10,321
Net Income					4,848	5,264	5,830	4,062	20,691	20,004	13,478
Less: Net income attributable to the noncontrolling interest					0	0	0	0	0	0	327
Net Income Attributable to Northrim BanCorp, Inc.	4,580	$ 7,538	$ 4,261	$ 4,312	4,848	$ 5,264	$ 5,830	$ 4,062	20,691	20,004	13,151
Total assets	1,643,996				1,502,988				1,643,996	1,502,988	1,518,596
Loans held for sale	67,834				34,710				67,834	34,710	43,979
Community Banking
Segment Reporting Information [Line Items]
Total interest income									67,770	62,097	58,308
Interest expense									4,569	2,370	1,860
Net Interest Income									63,201	59,727	56,448
Provision (benefit) for loan losses									(1,175)	(500)	3,200
Total Other Operating Income									13,145	11,323	17,187
Compensation expense - RML acquisition payments									468	0	130
Other operating expense									54,520	49,956	50,271
Income Before Provision for Income Taxes									22,533	21,594	20,034
Provision for income taxes									4,408	3,361	9,499
Net Income									18,125	18,233	10,535
Less: Net income attributable to the noncontrolling interest											327
Net Income Attributable to Northrim BanCorp, Inc.											10,208
Total assets	1,540,869				1,443,745				1,540,869	1,443,745	1,452,602
Loans held for sale	0				0				0	0	0
Home Mortgage Lending
Segment Reporting Information [Line Items]
Total interest income									2,313	2,080	1,800
Interest expense									1,072	599	570
Net Interest Income									1,241	1,481	1,230
Provision (benefit) for loan losses									0	0	0
Total Other Operating Income									24,201	20,844	23,287
Compensation expense - RML acquisition payments									0	0	0
Other operating expense									21,850	19,844	20,752
Income Before Provision for Income Taxes									3,592	2,481	3,765
Provision for income taxes									1,026	710	822
Net Income									2,566	1,771	2,943
Less: Net income attributable to the noncontrolling interest											0
Net Income Attributable to Northrim BanCorp, Inc.											2,943
Total assets	103,127				59,243				103,127	59,243	65,994
Loans held for sale	$ 67,834				$ 34,710				$ 67,834	$ 34,710	$ 43,979