BUSINESS COMBINATIONS - Additional Information (Details) - USD ($) $ in Thousands					12 Months Ended
	Nov. 03, 2017	Oct. 20, 2017	Apr. 07, 2017	Mar. 11, 2016	Dec. 31, 2017	Dec. 31, 2016	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							$ 314,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable							63,000
Business Acquisition Intangible Assets Expected Tax Deductible Amount							$ 13,000
Business Loan Premium							0.50%
Business Combination, Acquisition Related Costs					$ 12,900	$ 9,000
Floridian Financial Group [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets				$ 417,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits				337,000
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans				266,000
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 equals 35% cash and 65% Seacoast shares (based on Seacoast’s closing price of $15.47 per share on March 11, 2016).
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount				$ 32,000
BMO Harris Central [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets							$ 314,000
Gulf Shore Banc shares Inc [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets			$ 358,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits			285,000
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans			251,000
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 Seacoast’s closing price of $23.94 per share on April 7, 2017).
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount			$ 37,100
Gulf Shore Banc shares Inc [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired					100.00%
Palm Beach Community Bank [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	$ 9,909
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits	269,000
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans	$ 272,000
Business Acquisition, Equity Interest Issued or Issuable, Description	Under the terms of the definitive agreement, PBCB shareholders received, for each share of PBCB common stock, the combination of $6.26 in cash and 0.9240 shares of Seacoast common stock (based on Seacoasts closing price of $24.31 per share on November 3, 2017).
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Loan Held For Sale	$ 272,090
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	268,633
Business Acquisition Intangible Assets Tax Deductible Period					15 years
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount	$ 33,400
NorthStar Bank [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		$ 216,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits		182,000
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans		$ 137,000
Business Acquisition, Equity Interest Issued or Issuable, Description		Under the terms of the definitive agreement, NSBC shareholders received, for each share of NSBC common stock, the combination of $2.40 in cash and 0.5605 shares of Seacoast common stock (based on Seacoasts closing price of $24.92 per share on October 20, 2017)
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount		$ 12,400