Employee Benefit Plans (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) plan shares	Mar. 31, 2020 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 288	$ 251
Number of stock option plans | plan	1
Deferred tax expense from stock options exercised	$ 1	$ 23
Unrecognized compensation cost	$ 0
Shares vested (in shares) | shares	0	0
Stock Options [Member]
Defined Benefit Plan Disclosure [Line Items]
Options, exercises in period, intrinsic value	$ 192	$ 65
Options, outstanding, intrinsic value	944
Proceeds from options exercised	147
Stock Appreciation Rights (SARs) [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based compensation expense	$ 49
Share-based compensation income		118
Granted (in shares) | shares	22,000
Restricted Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based compensation expense	$ 201	$ 110
Unrecognized compensation cost	$ 1,800
Unrecognized compensation costs, period for recognition	3 years 2 months 8 days
Grant-date fair value	$ 88
Vested (in shares) | shares	3,918
2015 Stock Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Rights issued (in shares) | shares	21,886
Rights available for grant (in shares) | shares	1,834,427
Cornerstone Bancshares, Inc. Long-Term Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Rights issued (in shares) | shares	19,250
Cornerstone Non-Qualified Plan Options [Member]
Defined Benefit Plan Disclosure [Line Items]
Rights issued (in shares) | shares	40,250
Capstone Stock Option Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Rights issued (in shares) | shares	2,266
401 (k) Matching Range One [Member] | Deferred Salary Reduction Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match	100.00%
Employer matching contribution, percent of employees gross pay	3.00%
401 (k) Matching Range Two [Member] | Deferred Salary Reduction Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match	50.00%
Employer matching contribution, percent of employees gross pay	2.00%