CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Interest-bearing deposits in banks and other financial institutions, collateral	$ 4,500	$ 3,380
Available-for-sale securities, amortized cost basis	933,678	847,791
Held-to-maturity securities, fair value	159,164	162,853
Allowance for loan losses	$ 40,810	$ 40,599
Common stock, shares authorized (in shares)	65,000,000	65,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, issued (in shares)	56,394,559	56,279,527
Treasury stock, shares (in shares)	24,391,145	24,861,145