BUSINESS COMBINATIONS - Narrative (Details) $ / shares in Units, $ in Thousands						1 Months Ended	3 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 ($) transaction	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) shares	Jun. 30, 2019 USD ($)	Jan. 30, 2018 USD ($)
Business Acquisition [Line Items]
Issuance of common stock in acquisitions									$ 0	$ 869,294	$ 547,127
Goodwill							$ 503,434		928,005	931,637	503,434
Other noninterest income									17,133	$ 18,150	$ 12,968
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
Common shares issued in a business combination (in shares) | shares	22,181,522
Issuance of common stock in acquisitions	$ 869,300
Goodwill									426,865
Loans	3,510,000								3,512,262
Loan discount	$ 75,200
Loan discount, percent	2.09%
Accretable yield	$ 121,300
Cash exchanged for shares	19
Company common stock issued	869,294
Purchase price	$ 869,313
Fidelity Southern Corporation | Georgia
Business Acquisition [Line Items]
Number of bank branches | branch	46
Fidelity Southern Corporation | Florida
Business Acquisition [Line Items]
Number of bank branches | branch	16
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
Common shares issued in a business combination (in shares) | shares		6,548,385
Issuance of common stock in acquisitions		$ 349,356
Goodwill									220,768
Loans		1,290,000							1,293,186
Loan discount		$ 21,100
Loan discount, percent		1.60%
Accretable yield		$ 18,600
Cash consideration distributed per share to shareholders of acquiree (USD per share) | $ / shares		$ 0.93
Cash exchanged for shares		$ 47,779
Company common stock issued		349,400
Purchase price		$ 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
Common shares issued in a business combination (in shares) | shares			2,631,520
Goodwill									90,342
Loans			$ 755,700						755,704
Loan discount			$ 21,900
Loan discount, percent			2.82%
Accretable yield			$ 10,800
Cash consideration distributed per share to shareholders of acquiree (USD per share) | $ / shares			$ 1.39
Cash exchanged for shares			$ 21,527
Company common stock issued			147,760
Purchase price			$ 169,287
US Premium Financing Holding Company
Business Acquisition [Line Items]
Common shares issued in a business combination (in shares) | shares				830,301								1,073,158
Issuance of common stock in acquisitions												$ 55,855
Goodwill									$ 64,498
Cash exchanged for shares												$ 21,421
Company common stock issued				$ 44,500	$ 5,500
Purchase of remaining ownership interest in cost method investment				70.00%	25.01%	70.00%						70.00%
Number of acquisition transactions | transaction						3
Contingent consideration, maximum				$ 5,800		$ 5,800						$ 5,800
Contingent consideration paid													$ 1,200
Present value of contingent earn-out consideration expected to be paid												5,705
Purchase price				$ 8,900	$ 12,500							$ 82,981
Other noninterest income							$ 2,500	$ 2,000
US Premium Financing Holding Company
Business Acquisition [Line Items]
Ownership percentage														30.00%
Equity securities														$ 23,900