Parent Company Information - Statements Of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income
Interest income	$ 15,232	$ 15,519	$ 14,892	$ 14,465	$ 14,522	$ 14,860	$ 14,718	$ 14,818	$ 60,108	$ 58,918	$ 59,780
Other income	7,952	13,855	9,762	8,905	10,359	11,935	11,864	9,105	40,474	43,263	44,608
Expense
Interest expense	548	602	648	632	631	647	639	644	2,430	2,561	2,871
Income Before Provision for Income Taxes	4,299	8,581	5,196	5,723	5,153	4,310	6,374	5,205	23,799	21,042	27,118
Benefit from income taxes	4,085	2,980	1,455	1,801	1,458	1,027	1,868	1,699	10,321	6,052	8,784
Net income attributable to Northrim BanCorp, Inc.	$ 214	$ 5,523	$ 3,589	$ 3,825	$ 3,590	$ 3,095	$ 4,350	$ 3,376	13,151	14,411	17,783
Northrim Bancorp, Inc.
Income
Interest income									408	369	116
Equity in undistributed earnings from subsidiaries									14,101	15,396	19,005
Other income									52	0	175
Total Income									14,585	15,765	19,296
Expense
Interest expense									516	534	463
Administrative and other expenses									2,242	2,382	2,191
Total Expense									2,758	2,916	2,654
Income Before Provision for Income Taxes									11,827	12,849	16,642
Benefit from income taxes									(1,324)	(1,562)	(1,141)
Net income attributable to Northrim BanCorp, Inc.									13,151	14,411	17,783
Northrim Bancorp, Inc. | Northrim Bank
Income
Equity in undistributed earnings from subsidiaries									14,003	15,301	18,865
Northrim Bancorp, Inc. | Northrim Investment Services Company
Income
Equity in undistributed earnings from subsidiaries									$ 122	$ 95	$ 140