Fair Value of Financial Instruments - Carrying Amounts and Estimated Fair Values of Selected Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Securities held-to-maturity, amortized cost	$ 58,739	$ 58,888
Securities available for sale, fair value	647,974	772,500
Interest Rate Swap [Member]
Interest Rate Swaps, Net Amount	1,319	2,352
Interest rate swaps	(2,629)	388
Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity, amortized cost	7,914	7,934
Securities available for sale, fair value	404,460	523,849
Other Debt Obligations [Member]
Securities held-to-maturity, amortized cost	49,918	50,954
Securities available for sale, fair value	243,514	248,651
Reported Value Measurement [Member]
Cash and due from banks	157,388	49,787
Loans	6,704,674	5,772,206
FHLB-NY stock	43,439	56,921
Accrued interest receivable	44,041	25,722
Deposits	6,136,355	5,066,424
Borrowings	1,020,895	1,237,231
Accrued interest payable	4,755	6,752
Reported Value Measurement [Member] \| Interest Rate Swap [Member]
Interest Rate Swaps, Net Amount	1,319	2,352
Interest rate swaps	60,987	19,653
Reported Value Measurement [Member] \| Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity, amortized cost	7,914	7,934
Securities available for sale, fair value	404,460	523,849
Reported Value Measurement [Member] \| Other Debt Obligations [Member]
Securities held-to-maturity, amortized cost	49,918	50,954
Securities available for sale, fair value	243,514	248,651
Estimate of Fair Value Measurement [Member]
Cash and due from banks	157,388	49,787
Loans	6,793,985	5,822,124
FHLB-NY stock	43,439	56,921
Accrued interest receivable	44,041	25,722
Deposits	6,141,775	5,070,046
Borrowings	1,017,573	1,389,883
Accrued interest payable	4,755	6,752
Estimate of Fair Value Measurement [Member] \| Interest Rate Swap [Member]
Interest Rate Swaps, Net Amount	1,319	2,352
Interest rate swaps	60,987	19,653
Estimate of Fair Value Measurement [Member] \| Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity, amortized cost	8,991	8,114
Securities available for sale, fair value	404,460	523,849
Estimate of Fair Value Measurement [Member] \| Other Debt Obligations [Member]
Securities held-to-maturity, amortized cost	54,538	53,998
Securities available for sale, fair value	243,514	248,651
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and due from banks	157,388	49,787
Accrued interest receivable	2	9
Deposits	4,997,994	3,628,534
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other Debt Obligations [Member]
Securities available for sale, fair value	12,703	12,216
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
FHLB-NY stock	43,439	56,921
Accrued interest receivable	1,389	2,519
Deposits	1,143,781	1,441,512
Borrowings	974,437	1,345,499
Accrued interest payable	4,755	6,752
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Interest Rate Swaps, Net Amount	1,319	2,352
Interest rate swaps	60,987	19,653
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity, amortized cost	8,991	8,114
Securities available for sale, fair value	404,460	523,849
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other Debt Obligations [Member]
Securities available for sale, fair value	229,516	235,103
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Loans	6,793,985	5,822,124
Accrued interest receivable	42,650	23,194
Borrowings	43,136	44,384
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other Debt Obligations [Member]
Securities held-to-maturity, amortized cost	54,538	53,998
Securities available for sale, fair value	$ 1,295	$ 1,332

Fair value portion of accrued interest payable.

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Fair value portion of accrued interest receivable.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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