Consolidated statements of changes in shareholders' equity - USD ($) $ in Thousands	Total	FNB Financial Corp.	Franklin Financial Network, Inc.	Cumulative effect of change in accounting principle	Adjusted balance	Common stock	Common stock FNB Financial Corp.	Common stock Franklin Financial Network, Inc.	Common stock Adjusted balance	Additional paid-in capital	Additional paid-in capital FNB Financial Corp.	Additional paid-in capital Franklin Financial Network, Inc.	Additional paid-in capital Adjusted balance	Retained earnings	Retained earnings Cumulative effect of change in accounting principle	Retained earnings Adjusted balance	Accumulated other comprehensive income, net	Accumulated other comprehensive income, net Adjusted balance	Total common shareholders' equity	Total common shareholders' equity FNB Financial Corp.	Total common shareholders' equity Franklin Financial Network, Inc.	Total common shareholders' equity Cumulative effect of change in accounting principle	Total common shareholders' equity Adjusted balance	Noncontrolling interests	Noncontrolling interests Franklin Financial Network, Inc.	Noncontrolling interests Adjusted balance
Beginning balance at Dec. 31, 2018	$ 671,857			$ (1,309)	$ 670,548	$ 30,725			$ 30,725	$ 424,146			$ 424,146	$ 221,213	$ (1,309)	$ 219,904	$ (4,227)	$ (4,227)	$ 671,857			$ (1,309)	$ 670,548	$ 0		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to FB Financial Corporation and noncontrolling interest	83,814													83,814					83,814
Other comprehensive income, net of taxes	16,365																16,365		16,365
Stock based compensation expense	7,089					12				7,077									7,089
Restricted stock units vested and distributed, net of shares withheld	(6,097)					274				(6,371)									(6,097)
Shares issued under employee stock purchase program	804					23				781									804
Dividends declared	(10,194)													(10,194)					(10,194)
Ending balance at Dec. 31, 2019	762,329			$ (25,018)	$ 737,311	31,034			$ 31,034	425,633			$ 425,633	293,524	$ (25,018)	$ 268,506	12,138	$ 12,138	762,329			$ (25,018)	$ 737,311	0		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to FB Financial Corporation and noncontrolling interest	63,629													63,621					63,621					8
Other comprehensive income, net of taxes	15,457																15,457		15,457
Common stock issued in connection with acquisitions, net of registration costs (See Note 2)		$ 34,847	$ 444,966				$ 955	$ 15,058			$ 33,892	$ 429,815								$ 34,847	$ 444,873				$ 93
Stock based compensation expense	10,214					22				10,192									10,214
Restricted stock units vested and distributed, net of shares withheld	(1,510)					123				(1,633)									(1,510)
Shares issued under employee stock purchase program	978					30				948									978
Dividends declared	(14,502)													(14,502)					(14,502)
Noncontrolling interest distribution	(8)																							(8)
Ending balance at Dec. 31, 2020	1,291,382					47,222				898,847				317,625			27,595		1,291,289					93
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to FB Financial Corporation and noncontrolling interest	190,301													190,285					190,285					16
Other comprehensive income, net of taxes	(21,737)																(21,737)		(21,737)
Repurchase of common stock	(7,595)					(179)				(7,416)									(7,595)
Stock based compensation expense	10,282					7				10,275									10,282
Restricted stock units vested and distributed, net of shares withheld	(10,158)					462				(10,620)									(10,158)
Shares issued under employee stock purchase program	1,480					37				1,443									1,480
Dividends declared	(21,244)													(21,244)					(21,244)
Noncontrolling interest distribution	(16)																							(16)
Ending balance at Dec. 31, 2021	$ 1,432,695					$ 47,549				$ 892,529				$ 486,666			$ 5,858		$ 1,432,602					$ 93