Securities (Carrying Value of Securities Pledged as Collateral) (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	$ 402,067
Washington and Oregon State Public Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	246,950
Federal Reserve Bank Advances [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	52,754
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	$ 102,363