CONSOLIDATED STATEMENTS OF CONDITION (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Investments held-to-maturity, fair value	$ 217,880	$ 222,260
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	24,562,471	25,044,877
Common stock, shares outstanding	24,562,471	25,044,877