CONSOLIDATED STATEMENTS OF CONDITION (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Investments held-to-maturity, fair value		$ 211,704
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	23,827,305	24,295,971
Common stock, shares outstanding	23,827,305	24,295,971