CONSOLIDATED STATEMENTS OF CONDITION (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets:
Available-for-sale investment securities, cost	$ 3,011,551	$ 2,952,278
Equity and other securities, cost	$ 42,965	$ 44,678
Shareholders' equity:
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized (in shares)	500,000	500,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	75,000,000	75,000,000
Common stock, shares issued (in shares)	51,974,726	51,576,839
Treasury stock, at cost (in shares)	180,803	319,015
Shares held by deferred compensation arrangements (in shares)	179,548	207,403