Shareholders' Equity - Summary of Required Regulatory Capital (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to risk-weighted assets), Amount		$ 619,746	$ 432,058
Total Capital (to risk-weighted assets), Ratio		14.24%	13.25%
Total Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Amount	[1]	$ 348,191	$ 260,790
Total Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Ratio	[1]	8.00%	8.00%
Tier 1 Capital (to risk-weighted assets), Amount		$ 592,562	$ 408,596
Tier 1 Capital (to risk-weighted assets), Ratio		13.61%	12.53%
Tier 1 Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Amount	[1]	$ 261,143	$ 195,592
Tier 1 Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Ratio	[1]	6.00%	6.00%
Common Equity Tier 1 Capital (to risk-weighted assets), Amount		$ 523,832	$ 351,769
Common Equity Tier 1 Capital (to risk-weighted assets), Ratio		12.04%	10.79%
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum for Capital, Adequacy Purpose, Amount	[1]	$ 195,858	$ 146,694
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum for Capital, Adequacy Purpose, Ratio	[1]	4.50%	4.50%
Trust preferred securities issued		$ 592,562	$ 408,596
Tier 1 Capital (to adjusted average assets), Ratio		10.68%	9.15%
Tier 1 Capital (to adjusted average assets), Minimum for Capital Adequacy Purpose, Amount	[1]	$ 221,863	$ 178,656
Tier 1 Capital (to adjusted average assets), Minimum for Capital Adequacy Purpose, Ratio	[1]	4.00%	4.00%
Seacoast National Bank (A Wholly Owned Bank Subsidiary) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to risk-weighted assets), Amount		$ 565,149	$ 415,147
Total Capital (to risk-weighted assets), Ratio		13.04%	12.75%
Total Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Amount	[1]	$ 346,780	$ 260,491
Total Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Ratio	[1]	8.00%	8.00%
Tier 1 Capital (to risk-weighted assets), Amount		$ 537,965	$ 391,685
Tier 1 Capital (to risk-weighted assets), Ratio		12.41%	12.03%
Tier 1 Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Amount	[1]	$ 260,085	$ 195,368
Tier 1 Capital (to risk-weighted assets), Minimum for Capital Adequacy Purpose, Ratio	[1]	6.00%	6.00%
Common Equity Tier 1 Capital (to risk-weighted assets), Amount		$ 537,965	$ 391,685
Common Equity Tier 1 Capital (to risk-weighted assets), Ratio		12.41%	12.03%
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum for Capital, Adequacy Purpose, Amount	[1]	$ 195,022	$ 146,526
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum for Capital, Adequacy Purpose, Ratio	[1]	4.50%	4.50%
Trust preferred securities issued		$ 537,965	$ 391,685
Tier 1 Capital (to adjusted average assets), Ratio		9.72%	8.78%
Tier 1 Capital (to adjusted average assets), Minimum for Capital Adequacy Purpose, Amount	[1]	$ 221,432	$ 178,501
Tier 1 Capital (to adjusted average assets), Minimum for Capital Adequacy Purpose, Ratio	[1]	4.00%	4.00%
Total Capital (to risk-weighted assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		$ 433,475	$ 325,987
Total Capital (to risk-weighted assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	[1]	10.00%	10.00%
Tier 1 Capital (to risk-weighted assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		$ 346,780	$ 260,790
Tier 1 Capital (to risk-weighted assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	[1]	8.00%	8.00%
Tier 1 Capital (to adjusted average assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		$ 276,791	$ 223,320
Tier 1 Capital (to adjusted average assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	[1]	5.00%	5.00%
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		$ 281,759	$ 211,892
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	[1]	6.50%	6.50%

[1] Excludes capital conservation buffer of 1.250% the Company is subject to, which if not exceeded may constrain dividends, equity repurchases and compensation.