Acquisitions - Schedule of Acquired Loans not Deemed to Have Credit Impairment (Details) - USD ($) $ in Millions	Aug. 16, 2018	May 30, 2017
Inland Northwest Bank
Business Acquisition [Line Items]
Contractually required principal and interest payments	$ 894.8
Contractual cash flows not expected to be collected	26.1
Fair value at acquisition	$ 693.2
Bank of the Cascades
Business Acquisition [Line Items]
Contractually required principal and interest payments		$ 2,098.1
Contractual cash flows not expected to be collected		23.3
Fair value at acquisition		$ 2,066.5