Employee Benefit Plans - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) plan shares	Sep. 30, 2019 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 282	$ 187	$ 840	$ 602
Number of stock option plans | plan			1
Shares vested (in shares) | shares			0	0
Deferred tax expense from stock options exercised	3	10	$ 19	$ 37
Unrecognized compensation costs for non-vested restricted stock	0		0
Stock Options [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based compensation expense		58	0	122
Options, exercises in period, intrinsic value	75	53	141	165
Options, outstanding, intrinsic value	401		401
Proceeds from stock options exercised			282
Stock Appreciation Rights (SARs) [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based compensation expense				73
Sahre-based compensation income	(63)	(7)	(89)
Restricted Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based compensation expense	142	$ 95	365	$ 310
Unrecognized compensation costs for non-vested restricted stock	$ 1,100		$ 1,100
Unrecognized compensation costs, period for recognition			3 years 1 month 6 days
Grant date fair value of vested restricted stock			$ 134
Restricted stock vested (in shares) | shares			7,295
2015 Stock Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares issued (in shares) | shares			28,549
Number of shares available for grant (in shares) | shares	1,878,894		1,878,894
Legacy Cornerstone Bancshares, Inc. Long-Term Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares issued (in shares) | shares			33,250
Cornerstone Non-Qualified Plan Options [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares issued (in shares) | shares			41,250
Legacy Capstone Stock Option Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares 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%