Employee Benefit Plans - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Share-based compensation expense	$ 23,718	$ 33,000	$ 50,530	$ 66,635
Options vested in period, fair value			0	16,800
Deferred tax expense from stock options exercised			0	0
Options, exercises in period, intrinsic value			5,135,088
Options, outstanding, intrinsic value	2,692,426		2,692,426
Options, exercisable, intrinsic value	2,351,226		2,351,226
Proceeds from stock options exercised			$ 4,625,012
Number of shares granted			0		0
Deferred Salary Reduction Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	106,130	$ 99,568	$ 208,846	190,423
Director [Member]
Defined Benefit Plan Disclosure [Line Items]
Direct stock grant expense			31,791	$ 0
Stock Options [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation costs	$ 316,824		$ 316,824
Unrecognized compensation costs, period for recognition			1 year 3 months 22 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]
Exercise price, not less than (as a percent)			100.00%
Number of shares authorized	525,000		525,000
Legacy Smart Financial Inc 2010 Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Exercise price, not less than (as a percent)			100.00%
Number of shares authorized	525,000		525,000
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		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]
Requisite service period			1 year
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%