BUSINESS COMBINATIONS - Narrative (Details) $ / shares in Units, $ in Thousands							1 Months Ended	3 Months Ended		12 Months Ended
	Jun. 29, 2018 USD ($) branch $ / shares shares	May 25, 2018 USD ($) branch $ / shares shares	Jan. 31, 2018 USD ($) $ / shares shares	Jan. 03, 2018 USD ($)	Jan. 18, 2017 USD ($)	Mar. 11, 2016 USD ($) branch $ / shares shares	Jan. 31, 2018 USD ($) transaction $ / shares	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2018 USD ($)	Jan. 30, 2018 USD ($)
Business Acquisition [Line Items]
Issuance of common stock in acquisitions										$ 547,127		$ 0	$ 72,455
Goodwill								$ 503,434		503,434		125,532	125,532
Other noninterest income										15,298		$ 6,369	$ 7,115
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
Cash consideration distributed per share to shareholders of acquiree (USD per share) | $ / shares	$ 0.93
Common shares issued in a business combination (in shares) | shares	6,548,385
Issuance of common stock in acquisitions	$ 349,356
Cash exchanged for shares	47,779
Goodwill								219,643		219,643
Loans								1,298,040		1,298,040
Loan discount	$ 16,200
Loan discount, percent	1.23%
Accretable yield	$ 18,339
Company common stock issued	349,400
Purchase price	$ 397,135
Share price (in dollars per share) | $ / shares	$ 53.35
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
Cash consideration distributed per share to shareholders of acquiree (USD per share) | $ / shares		$ 1.39
Common shares issued in a business combination (in shares) | shares		2,631,520
Cash exchanged for shares		$ 21,527
Goodwill								92,970		92,970				$ 93,000
Loans								755,704		755,704				$ 755,700
Loan discount		$ 21,900
Loan discount, percent		2.82%
Accretable yield		$ 10,800
Company common stock issued		147,760
Purchase price		$ 169,287
Share price (in dollars per share) | $ / shares		$ 56.15
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
Cash exchanged for shares											$ 21,421
Goodwill								65,290		$ 65,290
Company common stock issued			$ 44,500	$ 5,500	$ 5,800
Purchase of remaining ownership interest in cost method investment			70.00%	25.01%	4.99%		70.00%				70.00%
Number of acquisition transactions | transaction							3
Additional cash payments			$ 5,800				$ 5,800				$ 5,800
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
Share price (in dollars per share) | $ / shares			$ 53.55				$ 53.55				$ 53.55
Jacksonville Bancorp, Inc
Business Acquisition [Line Items]
Number of bank branches | branch						8
Number of stock for each share of Ameris common stock converted (in shares) | shares						0.5861
Common shares issued in a business combination (in shares) | shares						2,549,469
Issuance of common stock in acquisitions						$ 72,455
Cash exchanged for shares						23,937
Goodwill						35,485
Loans						401,638
Accretable yield						27,000
Purchase price						$ 96,392
Share price (in dollars per share) | $ / shares						$ 16.50
Stock allocation						75.00%
Cash allocation						25.00%
Loans purchased						$ 401,600
Discount on loans acquired						$ 15,200
Percentage of discount on loans acquired						3.64%
US Premium Financing Holding Company
Business Acquisition [Line Items]
Ownership percentage															30.00%
Equity securities															$ 23,900