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SHAREHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands							1 Months Ended		9 Months Ended		12 Months Ended
	Jun. 29, 2018	May 25, 2018	Jan. 31, 2018	Jan. 03, 2018	Mar. 06, 2017	Jan. 18, 2017	Jan. 31, 2018	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 31, 2018	Feb. 16, 2018	Mar. 13, 2017
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock									$ 0	$ 88,656
Payments for capital contribution								$ 110,000
Senior Subordinated Notes
Subsidiary, Sale of Stock [Line Items]
Debt instrument, interest rate, stated percentage													5.75%
Underwritten Public Offering
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares)					2,012,500
Shares issued, price per share (in dollars per share)					$ 46.50
Issuance of common stock					$ 88,700
Public offering deduction amount					$ 4,900
Hamilton State Bancshares, Inc.
Subsidiary, Sale of Stock [Line Items]
Ameris Bancorp common shares issued (in shares)	6,548,385
Share price (in dollars per share)	$ 53.35
Increase in shareholders' equity	$ 349,400
Consideration transferred	$ 397,135
Atlantic Coast Financial Corporation
Subsidiary, Sale of Stock [Line Items]
Ameris Bancorp common shares issued (in shares)		2,631,520
Share price (in dollars per share)		$ 56.15
Increase in shareholders' equity		$ 147,800
Consideration transferred		$ 169,287
US Premium Financing Holding Company
Subsidiary, Sale of Stock [Line Items]
Ameris Bancorp common shares issued (in shares)			830,301				1,073,158				1,073,158
Share price (in dollars per share)			$ 53.55				$ 53.55				$ 53.55
Increase in shareholders' equity			$ 44,500	$ 5,500		$ 5,800
Percentage of voting interests acquired			70.00%	25.01%		4.99%	70.00%				70.00%
Stock issued during period, purchase of assets (in shares)				114,285		128,572
Price per share of the Company's common stock (in dollars per share)				$ 48.55		$ 45.45
Consideration transferred			$ 8,900	$ 12,500							$ 82,981
Contingent consideration, maximum			$ 5,800				$ 5,800				$ 5,800
Number of shares registered for resale or other disposition												944,586