Securities (Carrying Value of Securities Pledged as Collateral) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	$ 526,643	$ 362,787
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	328,400	277,012
To Federal Reserve Bank To Secure Borrowings [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	41,146	42,694
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of securities pledged as collateral	$ 157,097	$ 43,081