BUSINESS COMBINATIONS - Narrative (Details) $ / shares in Units, $ in Thousands						1 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended	18 Months Ended
	Jul. 01, 2019 USD ($) branch shares	Jun. 29, 2018 USD ($) branch $ / shares shares	May 25, 2018 USD ($) branch $ / shares shares	Jan. 31, 2018 USD ($) shares	Jan. 03, 2018 USD ($)	Jan. 31, 2018 USD ($) transaction shares	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jan. 31, 2018 USD ($) shares	Jun. 30, 2019 USD ($)	Jan. 30, 2018 USD ($)	Jan. 18, 2017
Business Acquisition [Line Items]
Issuance of common stock in acquisitions											$ 869,294	$ 547,127
Goodwill							$ 911,488	$ 503,434	$ 505,604		911,488	505,604
Other noninterest income							9,301		$ 2,561		16,567	$ 10,442
US Premium Financing Holding Company
Business Acquisition [Line Items]
Ownership percentage															30.00%
Cost method investment															$ 23,900
Fidelity Southern Corporation
Business Acquisition [Line Items]
Number of bank branches | branch	62
Number of stock for each share of Ameris common stock converted (in shares) | shares	0.80
Ameris Bancorp common shares issued (in shares) | shares	22,181,522
Issuance of common stock in acquisitions	$ 869,294
Goodwill	410,300						410,348				410,348
Loans	3,510,000						$ 3,508,410				$ 3,508,410
Loan discount	$ 79,000
Loan discount, percent	2.20%
Purchased credit-impaired loans acquired	$ 119,300
Cash exchanged for shares	19
Consideration transferred	$ 869,313
Hamilton State Bancshares, Inc.
Business Acquisition [Line Items]
Number of bank branches | branch		28
Number of stock for each share of Ameris common stock converted (in shares) | shares		0.16
Ameris Bancorp common shares issued (in shares) | shares		6,548,385
Issuance of common stock in acquisitions		$ 349,356
Goodwill		220,800												$ 220,768
Loans		1,290,000												1,293,186
Loan discount		$ 21,100
Loan discount, percent		1.60%
Purchased credit-impaired loans acquired		$ 15,400
Cash consideration distributed per share to shareholders of acquiree (USD per share) | $ / shares		$ 0.93
Cash exchanged for shares		$ 47,779
Consideration transferred		$ 397,135
Atlantic Coast Financial Corporation
Business Acquisition [Line Items]
Number of bank branches | branch			12
Number of stock for each share of Ameris common stock converted (in shares) | shares			0.17
Ameris Bancorp common shares issued (in shares) | shares			2,631,520
Issuance of common stock in acquisitions			$ 147,760
Goodwill			90,300											90,342
Loans			755,700											755,704
Loan discount			$ 21,900
Loan discount, percent			2.82%
Purchased credit-impaired loans acquired			$ 10,800
Cash consideration distributed per share to shareholders of acquiree (USD per share) | $ / shares			$ 1.39
Cash exchanged for shares			$ 21,527
Consideration transferred			$ 169,287
US Premium Financing Holding Company
Business Acquisition [Line Items]
Ameris Bancorp common shares issued (in shares) | shares				830,301		1,073,158							1,073,158
Issuance of common stock in acquisitions						$ 55,900							$ 55,855
Goodwill				$ 64,498		64,498							64,498
Cash exchanged for shares						$ 21,400							$ 21,421
Percentage of voting interests acquired				70.00%	25.01%	70.00%							70.00%			4.99%
Number of acquisition transactions | transaction						3
Contingent consideration, maximum				$ 5,800		$ 5,800							$ 5,800
Contingent consideration paid														$ 1,200
Liability for USPF acquisition contingent consideration				5,700		$ 5,700							5,700
Consideration transferred				$ 8,900	$ 12,500								$ 82,981
Other noninterest income								$ 2,500		$ 2,000
Georgia | Fidelity Southern Corporation
Business Acquisition [Line Items]
Number of bank branches | branch	46
Florida | Fidelity Southern Corporation
Business Acquisition [Line Items]
Number of bank branches | branch	16