Summary of Significant Accounting Policies - Calculation Of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Net income attributable to Northrim BanCorp, Inc.	$ 3,590	$ 3,095	$ 4,350	$ 3,376	$ 4,106	$ 5,335	$ 4,781	$ 3,561	$ 14,411	$ 17,783	$ 17,408
Basic weighted average common shares outstanding (in shares)									6,883,663	6,859,209	6,761,328
Dilutive effect of potential common shares from awards granted under equity incentive program (in shares)									91,000	89,000	91,000
Total (in shares)									6,974,864	6,948,474	6,852,267
Earnings per common share
Earnings Per Share, Basic (in USD per share)	$ 0.52	$ 0.45	$ 0.63	$ 0.49	$ 0.60	$ 0.78	$ 0.70	$ 0.52	$ 2.09	$ 2.59	$ 2.57
Earnings Per Share, Diluted (in USD per share)	$ 0.51	$ 0.44	$ 0.63	$ 0.48	$ 0.59	$ 0.77	$ 0.69	$ 0.51	$ 2.06	$ 2.56	$ 2.54