Investment Securities - Schedule of Held-to-maturity, Allowance for Credit Loss (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Allowance for credit losses:
Ending balance	$ 6
State and political subdivisions
Allowance for credit losses:
Beginning balance	0
Provision for credit losses	(2)
Charge-offs, net	0
Ending balance	6
State and political subdivisions | Impact of adoption ASC 326
Allowance for credit losses:
Beginning balance	8
Foreign bonds
Allowance for credit losses:
Beginning balance	0
Provision for credit losses	0
Charge-offs, net	0
Ending balance	0
Foreign bonds | Impact of adoption ASC 326
Allowance for credit losses:
Beginning balance	$ 0