Parent Company only Condensed Financial Information - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Other assets	$ 53,149	$ 14,799
Total assets	3,896,162	4,249,439
LIABILITIES AND EQUITY
Subordinated notes	58,872	58,693
Shareholders’ equity	410,333	372,740
Total liabilities and equity	3,896,162	4,249,439
Franklin Financial Network, Inc.
ASSETS
Cash and cash equivalents	3,625	3,364
Investment in banking subsidiary	463,496	426,979
Investment in other subsidiaries	3,527	1,919
Other assets	1,841	1,617
Total assets	472,489	433,879
LIABILITIES AND EQUITY
Subordinated notes	58,872	58,693
Accrued expenses and other liabilities	3,284	2,446
Shareholders’ equity	410,333	372,740
Total liabilities and equity	$ 472,489	$ 433,879