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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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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