Summary of Significant Accounting Policies - Narrative (Details)		3 Months Ended								6 Months Ended	12 Months Ended			19 Months Ended	117 Months Ended	123 Months Ended	213 Months Ended
	Dec. 01, 2014 USD ($) owner	Dec. 31, 2018 USD ($) trust borrower	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) segment trust borrower shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Jun. 30, 2016 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) trust borrower	Dec. 31, 2018 USD ($) trust borrower	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)	Aug. 31, 2017	Dec. 31, 2008 USD ($)
Accounting Policy [Line Items]
Number of wholly-owned Trusts | trust		1									1					1	1
Number of operating segments | segment											2
Maturity period of securities at acquisition											90 days
Threshold for nonperforming loans individually evaluated for impairment											$ 50,000
Loan loss history used											5 years
Average holding of purchased receivables											1 year
Advertising, promotion and marketing expenses											$ 2,318,000	$ 2,566,000	$ 2,449,000
Anti-dilutive shares (in shares) | shares											44,721	0	0
Commercial and construction loans		$ 451,800,000				$ 424,800,000					$ 451,800,000	$ 424,800,000				$ 451,800,000	$ 451,800,000
Large borrowing relationships | borrower		27									27					27	27
Unfunded commitments to large borrowers		$ 97,700,000									$ 97,700,000					$ 97,700,000	$ 97,700,000
Goodwill		15,017,000				15,017,000					15,017,000	15,017,000				15,017,000	15,017,000
Compensation expense - RML acquisition payments						(193,000)	$ 149,000	$ 0	$ 174,000		0	130,000	$ 4,775,000
Reduction in net income						(214,000)	(5,601,000)	(3,741,000)	(3,922,000)		(20,004,000)	(13,478,000)	(14,990,000)
Commercial servicing revenue											1,422,000	372,000	322,000
Assets		1,502,988,000				1,518,596,000				$ 1,525,851,000	1,502,988,000	1,518,596,000	1,525,851,000			1,502,988,000	1,502,988,000
Total Premises and Equipment		59,948,000				57,322,000					59,948,000	57,322,000				59,948,000	59,948,000
Net income		4,848,000	$ 5,264,000	$ 5,830,000	$ 4,062,000	214,000	$ 5,523,000	$ 3,589,000	$ 3,825,000		20,004,000	13,151,000	14,411,000
RML
Accounting Policy [Line Items]
Number of former equity owners | owner	4
Voting interests acquired	76.50%
Number of former equity owners with continuing employment contracts | owner	3
Number of former equity owners that must continue employment under terms of acquisition agreement | owner	2
Accrued compensation expense related to acquisition payments											0
Accounting for Payments Made to Former Equity Owners | RML
Accounting Policy [Line Items]
Total purchase price	$ 22,200,000
Goodwill	7,500,000
Revenue Recognized From Commercial Servicing Activities
Accounting Policy [Line Items]
Commercial servicing revenue											1,000,000
Assets		737,000									737,000					737,000	737,000
Net income																	737,000
Misclassification
Accounting Policy [Line Items]
Assets		480,000									$ 480,000					480,000	480,000
Depreciation															$ 670,000
Net income																480,000
Lender Concentration Risk
Accounting Policy [Line Items]
Concentration risk, percent											40.00%
Land
Accounting Policy [Line Items]
Total Premises and Equipment		5,137,000				2,562,000					$ 5,137,000	2,562,000				5,137,000	5,137,000
Land | Misclassification
Accounting Policy [Line Items]
Total Premises and Equipment																					$ 2,600,000
Furniture and equipment
Accounting Policy [Line Items]
Total Premises and Equipment		10,917,000				8,323,000					10,917,000	8,323,000				10,917,000	10,917,000
Leasehold improvements
Accounting Policy [Line Items]
Total Premises and Equipment		8,268,000				8,323,000					$ 8,268,000	8,323,000				8,268,000	8,268,000
Buildings
Accounting Policy [Line Items]
Premises and equipment, useful life											39 years
Total Premises and Equipment		$ 35,626,000				38,114,000					$ 35,626,000	38,114,000				$ 35,626,000	$ 35,626,000
Buildings | Misclassification
Accounting Policy [Line Items]
Total Premises and Equipment																					$ (2,600,000)
Minimum | Furniture and equipment
Accounting Policy [Line Items]
Premises and equipment, useful life											3 years
Minimum | Leasehold improvements
Accounting Policy [Line Items]
Premises and equipment, useful life											2 years
Maximum | Furniture and equipment
Accounting Policy [Line Items]
Premises and equipment, useful life											7 years
Maximum | Leasehold improvements
Accounting Policy [Line Items]
Premises and equipment, useful life											15 years
Northrim Benefits Group
Accounting Policy [Line Items]
Equity interest percentage																				50.10%
Retained Earnings
Accounting Policy [Line Items]
Net income											$ 20,004,000	13,151,000	14,411,000
Accounting Standards Update 2016-01
Accounting Policy [Line Items]
Cumulative effect of new accounting principle in period of adoption																			$ 0
Accounting Standards Update 2016-01 | AOCI Attributable to Parent
Accounting Policy [Line Items]
Cumulative effect of new accounting principle in period of adoption						(191,000)						(191,000)							(191,000)
Accounting Standards Update 2016-01 | Retained Earnings
Accounting Policy [Line Items]
Cumulative effect of new accounting principle in period of adoption						$ 191,000						$ 191,000							191,000
Accounting Standards Update 2017-08
Accounting Policy [Line Items]
Cumulative effect of new accounting principle in period of adoption																			(62,000)
Accounting Standards Update 2017-08 | Retained Earnings
Accounting Policy [Line Items]
Cumulative effect of new accounting principle in period of adoption					$ (62,000)														$ (62,000)
Accounting Standards Update 2016-02 | Scenario, Forecast
Accounting Policy [Line Items]
Right-of-use asset																		$ 15,900,000
Lease liability																		$ 15,900,000
Restatement Adjustment | Accounting for Payments Made to Former Equity Owners | RML
Accounting Policy [Line Items]
Compensation expense - RML acquisition payments										765,000				$ 2,300,000
Reduction in net income										$ 438,000			$ 1,800,000	$ 1,400,000
Previously Reported | Accounting for Payments Made to Former Equity Owners | RML
Accounting Policy [Line Items]
Total purchase price	29,500,000
Goodwill	$ 14,800,000