Summary of Significant Accounting Policies (Details) shares in Thousands		12 Months Ended
	Oct. 30, 2020 USD ($)	Dec. 31, 2021 USD ($) item shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)
Other real estate owned		$ 0	$ 0	$ 239,000	$ 0
Cash and Cash Equivalents, at Carrying Value, Ending Balance		81,700,000	157,400,000
Restricted Cash and Cash Equivalents		$ 21,500,000	$ 63,500,000
Restricted Cash and Cash Equivalents, Asset, Statement of Financial Position [Extensible List]		Cash and Cash Equivalents, at Carrying Value, Ending Balance	Cash and Cash Equivalents, at Carrying Value, Ending Balance
Interest-bearing Deposits in Banks and Other Financial Institutions		$ 51,700,000	$ 133,700,000
Interest Income, Securities, Operating, Tax Exempt		1,700,000	1,900,000	2,000,000.0
Goodwill, Impairment Loss		0	0	0
Goodwill, Ending Balance		17,636,000	17,636,000
Financing Receivable Purchase		262,100,000	193,300,000	221,200,000
Financing Receivable Sale		27,400,000	7,400,000	13,700,000
(Benefit) provision for loans		4,900,000	22,600,000	2,800,000
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
Advertising Expense		$ 2,500,000	1,800,000	2,200,000
Number of business units | item		3
Purchase of bank owned life insurance		$ 25,000,000	$ 0	$ 25,000,000
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		$ 8,700,000	$ 5,900,000
Loans Receivable [Member]
Number of active forbearances | item		20
Outstanding balance in active forbearance		$ 71,900,000
Financing Receivable		4,800,000
Interest Receivable		$ 35,800,000	$ 41,500,000