Junior Subordinated Debentures (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2005	May 31, 2003
Subordinated Borrowing [Line Items]
Investment in unconsolidated trust	$ 58,076,000				$ 56,504,000				$ 58,076,000	$ 56,504,000
Junior subordinated debentures	10,310,000				10,310,000				10,310,000	10,310,000
Interest expense on deposits, borrowings and junior subordinated debentures	1,652,000	$ 1,531,000	$ 1,349,000	$ 1,109,000	$ 1,070,000	$ 761,000	$ 606,000	$ 532,000	5,641,000	2,969,000	$ 2,430,000
Northrim Capital Trust 1
Subordinated Borrowing [Line Items]
Investment in unconsolidated trust													$ 8,000,000
Junior subordinated debentures	$ 8,200,000								$ 8,200,000
LIBOR period									90 days
Basis plus LIBOR									3.15%
Liquidation preference per capital security (in USD per share)	$ 1,000								$ 1,000
Interest expense on deposits, borrowings and junior subordinated debentures									$ 0	0	219,000
Northrim Statutory Trust 2
Subordinated Borrowing [Line Items]
Investment in unconsolidated trust												$ 10,000,000
Junior subordinated debentures	$ 10,300,000								$ 10,300,000
LIBOR period									90 days
Basis plus LIBOR									1.37%
Liquidation preference per capital security (in USD per share)	$ 1,000								$ 1,000
Interest rate	3.26%								3.26%
Interest expense on deposits, borrowings and junior subordinated debentures									$ 398,000	$ 368,000	$ 268,000