Loans - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($) contract	Dec. 31, 2019 USD ($)	Aug. 21, 2020 USD ($)	Mar. 31, 2020 USD ($)	Mar. 13, 2020 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net deferred costs					$ 19,900,000
Accrued interest receivable	$ 31,300,000		$ 31,300,000		14,900,000
Loans in short-term payment deferral	15,400,000		15,400,000
Valuation allowance for loans in short-term payment deferral	400,000		400,000
Interest income from securities with no related allowance	100,000	$ 100,000	500,000	$ 1,200,000
Allowance for credit loss on TDRs	200,000	0	$ 200,000	$ 0
Number of loans under trouble debt restructuring | contract			4	3
Financing Receivable, Troubled Debt Restructuring, Subsequent Default			$ 1,400,000	$ 2,100,000
Interest income related to impaired loans with impairment measured on present value of expected future cash flows	19,000	$ 40,000	65,000	$ 102,000
Portfolio Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net deferred costs	21,800,000		21,800,000
Portfolio Loans | Paycheck Protection Program
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net deferred fees	$ 13,100,000		13,100,000
First Bank of the Palm Beaches
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans acquired in acquisition								$ 146,777,000
Fourth Street Banking Company
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans acquired in acquisition						$ 303,434,000
Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Remaining fair value adjustment for loans acquired			$ 34,600,000		$ 34,900,000
Percentage of fair value adjustment for loans acquired	3.00%		3.00%		3.80%
PCD Loans | First Bank of the Palm Beaches
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans acquired in acquisition							$ 43,000,000.0	$ 43,038,000
PCD Loans | Fourth Street Banking Company
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans acquired in acquisition	$ 49,400,000		$ 49,400,000			$ 49,373,000
Non-PCD Loans | First Bank of the Palm Beaches
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans acquired in acquisition							$ 103,800,000
Non-PCD Loans | Fourth Street Banking Company
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans acquired in acquisition	$ 254,100,000		$ 254,100,000