BUSINESS COMBINATIONS - Additional Information (Details) - USD ($) $ in Millions			3 Months Ended	6 Months Ended
	Apr. 07, 2017	Mar. 11, 2016	Jun. 30, 2017	Jun. 30, 2017	May 18, 2017	May 04, 2017	Jun. 03, 2016
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Premium Percentage							3.00%
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Loan Held For Sale							$ 314.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable							$ 63.0
Business Acquisition Intangible Assets Expected Tax Deductible Amount			$ 13.0	$ 13.0
Business Acquisition Intangible Assets Tax Deductible Period				15 years
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount		$ 32.0
Business Loan Premium							0.50%
Payments for Merger Related Costs			$ 4.3
Floridian Financial Group [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		417.0
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits		337.0
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans		$ 266.0
Business Acquisition, Equity Interest Issued or Issuable, Description				Under the terms of the definitive agreement, Floridian shareholders received, at their election, (i) the combination of $4.29 in cash and 0.5291 shares of Seacoast common stock, (ii) $12.25 in cash, or (iii) 0.8140 shares of Seacoast common stock, subject to a customary proration mechanism so that the aggregate consideration mix equaled 35% cash and 65% Seacoast shares (based on Seacoasts closing price of $15.47 per share on March 11, 2016).
Business Acquisition, Percentage of Voting Interests Acquired			100.00%	100.00%
Gulf Shore Banc shares Inc [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Description				Under the terms of the definitive agreement, GulfShore shareholders received, for each share of GulfShore common stock, the combination of $1.47 in cash and 0.4807 shares of Seacoast common stock (based on Seacoasts closing price of $23.94 per share on April 7, 2017).
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount	$ 37.0
Gulf Shore Banc shares Inc [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired			100.00%	100.00%
Palm Beach Community Bank [Member]
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits						$ 281.0
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans						$ 290.0
NorthStar Bank [Member]
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits					$ 168.0
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans					$ 137.0