Securities (Carrying Value of Securities Pledged as Collateral) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	$ 419,383	$ 398,889
To Washington and Oregon State To Secure Public Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	245,222	232,714
To Federal Reserve Bank To Secure Borrowings [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	52,917	33,825
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	$ 121,244	$ 132,350