Summary Of Significant Accounting Policies (Narrative) (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Oct. 01, 2020 USD ($)	Oct. 01, 2019 USD ($)	Sep. 30, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 185,148	$ 220,370
Restricted cash and cash equivalents	$ 54,600	33,300
Restricted cash and cash equivalents, balance sheet location	us-gaap:OtherAssets
Interest-bearing deposits held at the Federal Reserve Bank	$ 172,200	198,600
Average daily balance of required reserves at the Federal Reserve Bank	6,600	21,500
Cumulative effect of adopting ASU	1,284,859	1,336,326	$ 1,391,622			$ 1,368,313
Operating Lease, Right-of-Use Asset	14,700				$ 15,700
Operating Lease, Liability	$ 14,713				$ 15,500
Lease liability, balance sheet location	us-gaap:AccountsPayableAndOtherAccruedLiabilities				us-gaap:AccountsPayableAndOtherAccruedLiabilities
ACL	$ 31,527	9,226	$ 8,463			$ 8,398
Cumulative effect of adopting ASU [Member] | Accounting Standards Update 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of adopting ASU		$ 88
Forecast [Member]
Summary Of Significant Accounting Policies [Line Items]
ACL				$ 26,800
Reserves on unfunded commitments				7,800
Forecast [Member] | Cumulative effect of adopting ASU [Member] | Accounting Standards Update 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of adopting ASU				$ 2,300
Capital City Bancshares, Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Other intangible assets, estimated life			8 years
Traditional Banking Offices [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of Stores	45
In-Store Banking Offices [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of Stores	9