Parent Company Information - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 77,841	$ 50,551	$ 58,673	$ 68,556
Investment securities available for sale	312,750	331,219
Other assets	56,141	56,128
Total assets	1,519,109	1,526,540	1,499,492
LIABILITIES
Junior subordinated debentures	10,310	18,558
Other liabilities	22,606	21,672
Total liabilities	1,326,307	1,339,828
SHAREHOLDERS' EQUITY
Common stock	6,872	6,898
Additional paid-in capital	61,793	62,952
Retained earnings	124,407	117,141
Accumulated other comprehensive loss	(270)	(397)
Total Northrim BanCorp, Inc. shareholders' equity	192,802	186,594
Total liabilities and shareholders' equity	1,519,109	1,526,540
Northrim Bancorp, Inc.
ASSETS
Cash and cash equivalents	15,872	11,963	$ 10,258	$ 6,890
Investment securities available for sale	5,731	4,967
Other assets	1,951	2,248
Total assets	203,157	205,734
LIABILITIES
Junior subordinated debentures	10,310	18,558
Other liabilities	45	582
Total liabilities	10,355	19,140
SHAREHOLDERS' EQUITY
Common stock	6,872	6,898
Additional paid-in capital	61,793	62,952
Retained earnings	124,322	117,141
Accumulated other comprehensive loss	(185)	(397)
Total Northrim BanCorp, Inc. shareholders' equity	192,802	186,594
Total liabilities and shareholders' equity	203,157	205,734
Northrim Bancorp, Inc. | Northrim Bank
ASSETS
Investment in subsidiary	177,824	184,511
Northrim Bancorp, Inc. | Northrim Investment Services Company
ASSETS
Investment in subsidiary	1,469	1,487
Northrim Bancorp, Inc. | Northrim Capital Trust 1
ASSETS
Investment in subsidiary	0	248
Northrim Bancorp, Inc. | Northrim Statutory Trust 2
ASSETS
Investment in subsidiary	$ 310	$ 310