Fair Value Measurements - Book Value and Estimated Fair Value of Bank's Significant Financial Instruments Not Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financial Assets:
Securities held-to-maturity	$ 478,727	$ 397,763
Financial Liabilities:
Time deposits	471,414	255,423
Securities sold under agreements to repurchase with retail customers	69,078	75,872
Book Value [Member]
Financial Assets:
Cash and due from banks	311,583	43,946
Securities held-to-maturity	470,642	394,813
Federal Home Loan Bank of New York stock	18,289	19,978
Loans receivable, net and mortgage loans held for sale	3,050,375	1,973,400
Financial Liabilities:
Deposits other than time deposits	2,853,267	1,661,255
Time deposits	471,414	255,423
Securities sold under agreements to repurchase with retail customers	69,078	75,872
Federal Home Loan Bank advances and other borrowings	307,545	346,885
Level 1 Inputs [Member]
Financial Assets:
Cash and due from banks	311,583	43,946
Securities held-to-maturity	8,768
Financial Liabilities:
Securities sold under agreements to repurchase with retail customers	69,078	75,872
Level 2 Inputs [Member]
Financial Assets:
Securities held-to-maturity	469,959	397,763
Financial Liabilities:
Deposits other than time deposits	2,853,267	1,661,255
Time deposits	472,774	255,564
Federal Home Loan Bank advances and other borrowings	311,324	346,118
Level 3 Inputs [Member]
Financial Assets:
Federal Home Loan Bank of New York stock	18,289	19,978
Loans receivable, net and mortgage loans held for sale	$ 3,069,496	$ 1,986,891