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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Net income attributable to Northrim BanCorp, Inc.	$ 4,106	$ 5,335	$ 4,781	$ 3,561	$ 6,674	$ 3,707	$ 4,369	$ 2,658	$ 17,783	$ 17,408	$ 12,325
Basic weighted average common shares outstanding (shares)									6,859,209	6,761,328	6,518,772
Dilutive effect of potential common shares from awards granted under equity incentive program (shares)									89,000	91,000	91,000
Total (shares)									6,948,474	6,852,267	6,609,950
Earnings Per Share, Basic (USD per share)	$ 0.60	$ 0.78	$ 0.70	$ 0.52	$ 0.98	$ 0.54	$ 0.64	$ 0.41	$ 2.59	$ 2.57	$ 1.89
Earnings Per Share, Diluted (USD per share)	$ 0.59	$ 0.77	$ 0.69	$ 0.51	$ 0.97	$ 0.53	$ 0.63	$ 0.40	$ 2.56	$ 2.54	$ 1.87