Summary of Significant Accounting Policies (Details)		12 Months Ended
	Oct. 30, 2020 USD ($)	Dec. 31, 2022 USD ($) item security shares	Dec. 31, 2021 USD ($) security shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($)
Other real estate owned		$ 0	$ 0	$ 0	$ 239,000
Restricted Cash and Cash Equivalents		67,000,000.0	21,500,000
Cash (including restricted cash) held in excess of FDIC deposit insurance limits at other commercial banks		$ 73,900,000	$ 27,800,000
Number of securities in portfolio | security		4	3
Interest-bearing Deposits in Banks and Other Financial Institutions		$ 121,900,000	$ 51,700,000
Interest Income, Securities, Operating, Tax Exempt		1,700,000	1,700,000	1,900,000
Goodwill, Impairment Loss		0	0	0
Goodwill, Ending Balance		17,636,000	17,636,000
Financing Receivable Purchase		275,700,000	262,100,000	193,300,000
Financing Receivable Sale		32,000,000.0	28,600,000	7,500,000
(Benefit) provision for loans		4,842,000	(4,899,000)	22,563,000
Assets Acquired	$ 286,100,000
Allowance for credit losses	$ 4,100,000
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Ending Balance		0	0
Other than Temporary Impairment Losses, Investments, Total		0	0
Advertising Expense		$ 3,100,000	2,500,000	1,800,000
Number of business units | item		3
Purchase of bank owned life insurance		$ 0	$ 25,000,000	$ 0
Shares held in the Employee Benefit Trust | shares		0	17,964	39,861
Securities similar to commercial owner occupied loan
Number of securities in portfolio | security		2	1
Forbearance securities
Number of securities in portfolio | security		1	1
Securities issued and guaranteed by Fannie Mae
Number of securities in portfolio | security		1
Flushing Financial Capital Trust II [Member]
Capital Securities, Value Issued		$ 60,000,000.0
Common Securities With Voting Rights, Value , Issued		$ 1,900,000
Percentage Of Ownership Interest In Common Securities Of Trust		100.00%
Share-based Payment Arrangement, Option
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares		0	0	0
Bank Premises and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		3 years
Bank Premises and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life		10 years
Consumer Portfolio Segment [Member]
Mortgage Loans in Process of Foreclosure, Amount		$ 5,200,000	$ 8,700,000
Loans Receivable [Member]
Interest Receivable		$ 34,500,000	$ 35,800,000