Business Combinations - Additional Information (Details) - USD ($) $ in Millions			1 Months Ended	3 Months Ended
	Nov. 03, 2017	Apr. 07, 2017	Oct. 20, 2017	Mar. 31, 2018
Gulf Shore Banc shares Inc [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		$ 358.0
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits		285.0
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans		$ 251.0
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).
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount		$ 37.1
Palm Beach Community Bank [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	$ 357.0
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits	269.0
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans	$ 270.0
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%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount	$ 34.8
NorthStar Bank [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets			$ 216.0
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Deposits			182.0
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed Noncurrent Assets Loans			$ 137.0
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			$ 12.3