SHAREHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands								1 Months Ended	12 Months Ended				18 Months Ended
	Jul. 01, 2019	Jun. 29, 2018	May 25, 2018	Jan. 31, 2018	Jan. 03, 2018	Mar. 06, 2017	Jan. 18, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Jan. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Sep. 19, 2019	Feb. 16, 2018	Mar. 13, 2017
Subsidiary or Equity Method Investee [Line Items]
Repurchase amount									$ 18,410	$ 2,062		$ 886
Issuance of common stock									0	$ 0		$ 88,656
Payments for capital contribution								$ 110,000
Underwritten Public Offering
Subsidiary or Equity Method Investee [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
Senior Subordinated Notes
Subsidiary or Equity Method Investee [Line Items]
Interest rate, stated percentage																5.75%
Fidelity Southern Corporation
Subsidiary or Equity Method Investee [Line Items]
Common shares issued in a business combination (in shares)	22,181,522
Increase in shareholders' equity	$ 869,294
Share price (in dollars per share)	$ 39.19
Purchase price	$ 869,313
Hamilton State Bancshares, Inc.
Subsidiary or Equity Method Investee [Line Items]
Common shares issued in a business combination (in shares)		6,548,385
Increase in shareholders' equity		$ 349,400
Share price (in dollars per share)		$ 53.35
Purchase price		$ 397,135
Atlantic Coast Financial Corporation
Subsidiary or Equity Method Investee [Line Items]
Common shares issued in a business combination (in shares)			2,631,520
Increase in shareholders' equity			$ 147,760
Share price (in dollars per share)			$ 56.15
Purchase price			$ 169,287
US Premium Financing Holding Company
Subsidiary or Equity Method Investee [Line Items]
Common shares issued in a business combination (in shares)				830,301							1,073,158
Increase in shareholders' equity				$ 44,500	$ 5,500		$ 5,800
Share price (in dollars per share)				$ 53.55							$ 53.55
Purchase of remaining ownership interest in cost method investment				70.00%	25.01%		4.99%				70.00%
Stock issued during period, shares, 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
Purchase price				$ 8,900	$ 12,500						$ 82,981
Contingent consideration, maximum				$ 5,800							$ 5,800
Contingent consideration paid													$ 1,200
Number of shares registered for resale or other disposition (in shares)															944,586
Common Stock Repurchase Program, October 2020 Expiration
Subsidiary or Equity Method Investee [Line Items]
Authorized repurchase amount														$ 100,000
Repurchase amount									$ 6,800
Number of shares repurchased (in shares)									158,248
Common Stock Repurchase Program, October 2019 Expiration
Subsidiary or Equity Method Investee [Line Items]
Repurchase amount									$ 10,600
Number of shares repurchased (in shares)									296,335