CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
BALANCE (in shares) at Dec. 31, 2017		11,152,561
BALANCE at Dec. 31, 2017	$ 205,853	$ 11,153	$ 174,009	$ 21,889	$ (1,198)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	11,670			11,670
Other comprehensive income (loss)	(2,468)				(2,468)
Stock awards (in shares)		5,947
Stock awards	9	$ 6	3
Exercise of stock options (in shares)		132,783
Exercise of stock options	1,519	$ 133	1,386
Shareholders of TN Bancshares, Inc. (in shares)		1,458,981
Shareholders of TN Bancshares, Inc.	34,732	$ 1,459	33,273
Stock compensation expense	327		327
BALANCE (in shares) at Sep. 30, 2018		12,750,272
BALANCE at Sep. 30, 2018	251,642	$ 12,751	208,998	33,559	(3,666)
BALANCE (in shares) at Jun. 30, 2018		12,704,581
BALANCE at Jun. 30, 2018	247,487	$ 12,705	208,513	29,235	(2,966)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,324			4,324
Other comprehensive income (loss)	(700)				(700)
Stock awards (in shares)		5,553
Stock awards	0	$ 6	(6)
Exercise of stock options (in shares)		40,138
Exercise of stock options	447	$ 40	407
Stock compensation expense	84		84
BALANCE (in shares) at Sep. 30, 2018		12,750,272
BALANCE at Sep. 30, 2018	251,642	$ 12,751	208,998	33,559	(3,666)
BALANCE (in shares) at Dec. 31, 2018		13,933,504
BALANCE at Dec. 31, 2018	283,011	$ 13,933	231,852	39,991	(2,765)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,815			19,815
Other comprehensive income (loss)	2,468				2,468
Stock awards (in shares)		3,298
Stock awards	64	$ 3	61
Exercise of stock options (in shares)		21,171
Exercise of stock options	250	$ 22	228
Stock compensation expense	432		432
BALANCE (in shares) at Sep. 30, 2019		13,957,973
BALANCE at Sep. 30, 2019	306,040	$ 13,958	232,573	59,806	(297)
BALANCE (in shares) at Jun. 30, 2019		13,953,209
BALANCE at Jun. 30, 2019	299,611	$ 13,953	232,386	53,843	(571)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,963			5,963
Other comprehensive income (loss)	274				274
Exercise of stock options (in shares)		4,764
Exercise of stock options	38	$ 5	33
Stock compensation expense	154		154
BALANCE (in shares) at Sep. 30, 2019		13,957,973
BALANCE at Sep. 30, 2019	$ 306,040	$ 13,958	$ 232,573	$ 59,806	$ (297)