Loans and Allowance for Loan Losses - Age Analysis of Recorded Investment in Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Loans, Past Due	$ 67,381	$ 28,928
Loans, Current	6,637,293	5,728,007
Total loans	6,704,674	5,772,206
Loans	6,701,629	5,756,935
Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	36,947	8,219
Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	11,519	8,027
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	18,915	12,682
Multi-family Residential Portfolio Segment [Member]
Loans, Past Due	13,545	8,346
Loans, Current	2,522,432	2,230,245
Total loans	2,535,977
Loans		2,238,591
Multi-family Residential Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	7,582	4,042
Multi-family Residential Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	3,186	1,563
Multi-family Residential Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	2,777	2,741
Commercial Real Estate
Loans, Past Due	27,339	5,308
Loans, Current	1,731,045	1,576,700
Total loans	1,758,384
Loans		1,582,008
Commercial Real Estate \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	17,903	0
Commercial Real Estate \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	5,123	4,941
Commercial Real Estate \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	4,313	367
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member]
Loans, Past Due	8,238	1,887
Loans, Current	598,647	590,584
Total loans	606,885
Loans		592,471
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	5,673	1,117
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	1,132	496
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	1,433	274
One-To-Four Family - Residential Portfolio Segment [Member]
Loans, Past Due	9,205	6,881
Loans, Current	243,486	181,335
Total loans	252,691
Loans		188,216
One-To-Four Family - Residential Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	3,087	720
One-To-Four Family - Residential Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	805	1,022
One-To-Four Family - Residential Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	5,313	5,139
Co-Operative Apartments Portfolio Segment [Member]
Loans, Past Due	0	0
Loans, Current	0	8,663
Total loans	0
Loans		8,663
Co-Operative Apartments Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	0	0
Co-Operative Apartments Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	0	0
Co-Operative Apartments Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	0	0
Construction Portfolio Segment [Member]
Loans, Past Due	750	0
Loans, Current	82,411	67,754
Total loans	83,161
Loans	83,322	67,754
Construction Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	750	0
Construction Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	0	0
Construction Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	0	0
Small Business Administration Portfolio Segment [Member]
Loans, Past Due	2,991	1,151
Loans, Current	162,579	13,294
Total loans	165,570
Loans		14,445
Small Business Administration Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	1,823	0
Small Business Administration Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	0	0
Small Business Administration Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	1,168	1,151
Taxi Medallion Portfolio Segment [Member]
Loans, Past Due	2,318	1,065
Loans, Current	279	2,244
Total loans	2,597
Loans		3,309
Taxi Medallion Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	0	0
Taxi Medallion Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	0	0
Taxi Medallion Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	2,318	1,065
Commercial Business and Other Portfolio Segment [Member]
Loans, Past Due	2,995	4,290
Loans, Current	1,296,414	1,057,188
Total loans	1,299,409
Loans		1,061,478
Commercial Business and Other Portfolio Segment [Member] \| Financing Receivables, 30 to 59 Days Past Due [Member]
Loans, Past Due	129	2,340
Commercial Business and Other Portfolio Segment [Member] \| Financing Receivables, 60 to 89 Days Past Due [Member]
Loans, Past Due	1,273	5
Commercial Business and Other Portfolio Segment [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans, Past Due	$ 1,593	$ 1,945

Amount of financing receivable not past due.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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