Commitments and Contingent Liabilities (Details) - USD ($) $ in Thousands			12 Months Ended
	Aug. 11, 2017	Aug. 24, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Minimum future rental payments:
2019			$ 10,947
2020			9,766
2021			8,729
2022			8,102
2023			6,796
Thereafter			18,703
Total minimum payments			63,043
Operating Leases, Rent Expense, Sublease Rentals			1,200	$ 791	$ 992
Operating Leases, Rent Expense, Net			9,600	7,900	$ 8,700
Commitments to Extend Credit [Member]
Minimum future rental payments:
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability			2,620,000	2,620,000
Standby Letters of Credit [Member]
Minimum future rental payments:
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability			28,300	51,300
Commercial Letter of Credit and other off-balance sheet liabilities [Member]
Minimum future rental payments:
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability			0	$ 159
IDAHO
Minimum future rental payments:
Sale Leaseback Transaction, Date	August 11, 2017
Sale Leaseback Transaction, Monthly Rental Payments			26
Sale Leaseback Transaction, Deferred Gain, Gross	$ 509
Sale Leaseback Transaction, Deferred Gain, Net			444
WASHINGTON
Minimum future rental payments:
Sale Leaseback Transaction, Date		August 24, 2016
Sale Leaseback Transaction, Monthly Rental Payments			12
Sale Leaseback Transaction, Deferred Gain, Gross		$ 742
Sale Leaseback Transaction, Deferred Gain, Net			$ 575