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Fair Value Measurements - Estimated Fair Values of the Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Trading securities	$ 9,759	$ 8,968
Debt securities available-for-sale	894,272	808,031
Debt securities held-to-maturity	9,320	9,249
Financial liabilities:
Equity securities not been classified in the fair value	1,100	1,000
Carrying Value
Financial assets:
Cash and cash equivalents	85,825	77,762
Trading securities	9,759	8,968
Debt securities available-for-sale	894,272	808,031
Debt securities held-to-maturity	9,448	9,505
Equity securities	414	237
Federal Home Loan Bank of New York stock, at cost	22,517	22,517
Net loans held-for-investment	3,228,374	3,217,673
Financial liabilities:
Deposits	3,375,205	3,286,512
Borrowed funds	409,244	408,891
Advance payments by borrowers for taxes and insurance	20,723	18,007
Estimated Fair Value
Financial assets:
Cash and cash equivalents	85,825	77,762
Trading securities	9,759	8,968
Debt securities available-for-sale	894,272	808,031
Debt securities held-to-maturity	9,320	9,249
Equity securities	414	237
Federal Home Loan Bank of New York stock, at cost	22,517	22,517
Net loans held-for-investment	3,251,646	3,236,136
Financial liabilities:
Deposits	3,379,925	3,291,085
Borrowed funds	407,588	403,476
Advance payments by borrowers for taxes and insurance	20,723	18,007
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	85,825	77,762
Trading securities	9,759	8,968
Debt securities available-for-sale	0	0
Debt securities held-to-maturity	0	0
Equity securities	414	237
Federal Home Loan Bank of New York stock, at cost	0	0
Net loans held-for-investment	0	0
Financial liabilities:
Deposits	0	0
Borrowed funds	0	0
Advance payments by borrowers for taxes and insurance	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Trading securities	0	0
Debt securities available-for-sale	894,272	808,031
Debt securities held-to-maturity	9,320	9,249
Equity securities	0	0
Federal Home Loan Bank of New York stock, at cost	22,517	22,517
Net loans held-for-investment	0	0
Financial liabilities:
Deposits	3,379,925	3,291,085
Borrowed funds	407,588	403,476
Advance payments by borrowers for taxes and insurance	20,723	18,007
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Trading securities	0	0
Debt securities available-for-sale	0	0
Debt securities held-to-maturity	0	0
Equity securities	0
Federal Home Loan Bank of New York stock, at cost	0	0
Net loans held-for-investment	3,251,646	3,236,136
Financial liabilities:
Deposits	0	0
Borrowed funds	0	0
Advance payments by borrowers for taxes and insurance	$ 0	$ 0

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