Investment Securities - Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Amortized Cost	$ 267,977	$ 267,611
Fair Value	264,675	267,160
Washington and Oregon state to secure public deposits
Investment Holdings [Line Items]
Amortized Cost	199,026	206,377
Fair Value	196,786	206,425
Repurchase agreements
Investment Holdings [Line Items]
Amortized Cost	48,173	48,750
Fair Value	47,407	48,237
Other securities pledged
Investment Holdings [Line Items]
Amortized Cost	20,778	12,484
Fair Value	$ 20,482	$ 12,498