Consolidated Balance Sheet (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Pledged securities that can be sold or repledged	$ 470,906	$ 487,151
Investment securities, available for sale, amortized cost	10,508,620	10,938,796
Investment securities, held to maturity, fair value	3,160,215	3,341,762
Equity and other securities, cost	$ 526,593	$ 415,028
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	1,000,000	1,000,000
Common stock, par value	$ 0.50	$ 0.50
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	159,768,397	159,817,518
Common stock issuable, shares	24,371	27,138
Treasury stock, common shares	12,993,850	9,733,115
Series A And Series C [Member]
Preferred stock, shares issued	731,500	731,500
Preferred stock, shares outstanding	731,500	731,500
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Series D Preferred Stock [Member]
Preferred stock, shares issued	50,000	50,000
Preferred stock, shares outstanding	50,000	50,000
Preferred stock, liquidation preference per share	$ 10,000	$ 10,000