Employee Benefit Plans - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Share-based compensation expense	$ 26,812	$ 33,635
Options vested in period, fair value	0	19,425
Deferred tax expense from stock options exercised	0	0
Options, exercises in period, intrinsic value	5,024,759
Options, outstanding, intrinsic value	2,266,259
Options, exercisable, intrinsic value	2,034,800
Proceeds from stock options exercised	$ 4,260,734
Number of shares granted	0		0
Deferred Salary Reduction Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 102,716	$ 90,856
Director [Member]
Defined Benefit Plan Disclosure [Line Items]
Direct stock grant expense	31,791
Stock Options [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation costs	$ 340,542
Unrecognized compensation costs, period for recognition	1 year 4 months 24 days
Legacy Cornerstone Bancshares, Inc. Long-Term Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Exercise price, not less than (as a percent)	100.00%
Smart Bank Stock Option Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of shares authorized	525,000
Exercise price, not less than (as a percent)	100.00%
Legacy Smart Financial Inc 2010 Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of shares authorized	525,000
Exercise price, not less than (as a percent)	100.00%
Stock Incentive Plan Two Thousand Fifteen [Member]
Defined Benefit Plan Disclosure [Line Items]
Exercise price, not less than (as a percent)	110.00%
Number Outstanding (in shares)	2,000,000
Term of options, no more than	10 years
Voting power held by participant (as a percent)	10.00%
Term of option to participants with more than ten percent voting power	5 years
Percentage Of incentive stock options vesting on second anniversary	30.00%
Percentage Of incentive stock options vesting on third anniversary	30.00%
Percentage Of incentive stock options vesting on fourth anniversary	40.00%
Percentage Of nonqualified stock options vesting on first anniversary	50.00%
Percentage Of nonqualified stock options vesting on second anniversary	50.00%
401 (k) Matching Range One [Member] | Deferred Salary Reduction Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of employees gross pay	3.00%
Employer matching contribution, percent of match	100.00%
401 (k) Matching Range Two [Member] | Deferred Salary Reduction Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of employees gross pay	2.00%
Employer matching contribution, percent of match	50.00%