Outstanding Commitments and Contingent Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Credit Commitments and Contingencies
Liabilities for potential obligations under guarantees	$ 0	$ 0
Maximum
Credit Commitments and Contingencies
Term for guarantee	1 year
Commitments to extend credit
Credit Commitments and Contingencies
Financial instruments whose contract amounts represent credit risk	$ 1,296,406	1,300,294
Standby letters of credit
Credit Commitments and Contingencies
Financial instruments whose contract amounts represent credit risk	$ 33,244	$ 37,231