BUSINESS COMBINATIONS - Additional Information (Details) - USD ($)		9 Months Ended	12 Months Ended
	Mar. 11, 2016	Sep. 30, 2016	Dec. 31, 2015	Jun. 03, 2016	Jul. 17, 2015
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	$ 417,000,000
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				$ 314,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable				63,000,000
Business Acquisition Intangible Assets Expected Tax Deductible Amount				$ 13,000,000
Business Acquisition Intangible Assets Tax Deductible Period		15 years
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount	32,000,000
Business Loan Premium				0.50%
The Bank shares Inc [Member]
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits					$ 188,400,000
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans					$ 111,300,000
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Business Combination, Bargain Purchase, Gain Recognized, Amount			$ 416,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total			$ 2,600,000
The Bank shares Inc [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Stock Issued During Period, Value, Acquisitions		$ 18.7
Floridian Financial Group [Member]
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits	337,000,000
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans	$ 267,000,000
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 Seacoasts closing price of $15.47 per share on March 11, 2016).