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, 2017	Dec. 31, 2016
Financial Assets:
Securities held-to-maturity	$ 746,497	$ 598,119
Federal Home Loan Bank of New York stock, at cost	18,472	19,313
Financial Liabilities:
Time deposits	623,908	647,103
Securities sold under agreements to repurchase with deposit customers	75,326	69,935
Book Value
Financial Assets:
Cash and due from banks	255,258	301,373
Securities held-to-maturity	742,886	598,691
Federal Home Loan Bank of New York stock, at cost	18,472	19,313
Loans receivable, net and mortgage loans held for sale	3,870,447	3,804,994
Financial Liabilities:
Deposits other than time deposits	3,726,351	3,540,647
Time deposits	623,908	647,103
Securities sold under agreements to repurchase with deposit customers		69,935
Federal Home Loan Bank advances and other borrowings	315,652	307,057
Level 1 Inputs
Financial Assets:
Cash and due from banks	255,258	301,373
Securities held-to-maturity	8,714	8,550
Financial Liabilities:
Securities sold under agreements to repurchase with deposit customers	75,326	69,935
Level 2 Inputs
Financial Assets:
Securities held-to-maturity	734,990	586,504
Financial Liabilities:
Deposits other than time deposits	3,726,351	3,540,647
Time deposits	619,619	644,354
Federal Home Loan Bank advances and other borrowings	314,021	304,901
Level 3 Inputs
Financial Assets:
Securities held-to-maturity	2,793	3,030
Federal Home Loan Bank of New York stock	18,472	19,313
Loans receivable, net and mortgage loans held for sale	$ 3,935,093	$ 3,834,677