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Other Borrowings (Narrative) (Details) - USD ($)	9 Months Ended
Other Borrowings (Narrative) (Details) - USD ($)	Sep. 30, 2018	Feb. 28, 2018	Dec. 31, 2017	Dec. 31, 2008
Debt Instrument [Line Items]
Note payable	$ 9,665,000
Subordinated debt	$ 8,298,000		$ 4,232,000
First Tennessee Bank NA Variable Rate [Member]
Debt Instrument [Line Items]
Debt instrument maturity date	Feb. 28, 2023
Debt instrument, face amount	$ 5,000,000
Debt instrument, term	5 years
First Tennessee Bank NA Fixed Rate [Member]
Debt Instrument [Line Items]
Debt instrument maturity date	Feb. 28, 2023
Debt instrument, face amount	$ 5,000,000
Note payable	$ 4,700,000
Debt instrument, term	5 years
Interest rate	4.99%
Debt instrument, frequency of periodic payment	quarterly principal payments
Debt instrument, periodic payment, principal	$ 98,000
Universal Bancorp [Member]
Debt Instrument [Line Items]
Assumed debentures upon acquisition		$ 345,536,000
Medium-term Notes [Member] \| First Tennessee Bank NA [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		10,000,000
Medium-term Notes [Member] \| First Tennessee Bank NA Variable Rate [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, effective percentage	4.29%
3-Month LIBOR [Member] \| Medium-term Notes [Member] \| First Tennessee Bank NA Variable Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.95%
Pooled Trust Preferred Security [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, effective percentage	4.03%
Pooled Trust Preferred Security [Member] \| MFB Corporation [Member]
Debt Instrument [Line Items]
Assumed debentures upon acquisition				$ 5,000,000
Subordinated debt	$ 4,300,000
Pooled Trust Preferred Security [Member] \| Universal Bancorp [Member]
Debt Instrument [Line Items]
Assumed debentures upon acquisition		$ 5,000,000
Debt instrument maturity date	Oct. 07, 2035
Subordinated debt	$ 4,000,000
Pooled Trust Preferred Security [Member] \| Junior Subordinated Debt [Member] \| MFB Corporation [Member]
Debt Instrument [Line Items]
Debt instrument maturity date	Sep. 15, 2035
Pooled Trust Preferred Security [Member] \| 3-Month LIBOR [Member] \| Universal Bancorp [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.69%
Pooled Trust Preferred Security [Member] \| 3-Month LIBOR [Member] \| Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, effective percentage	4.03%
Pooled Trust Preferred Security [Member] \| 3-Month LIBOR [Member] \| Junior Subordinated Debt [Member] \| MFB Corporation [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	0.17%