Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Investment securities - held-to-maturity, fair value	$ 778,552	$ 433,201	$ 440,014
Common stock, stated value	$ 1	$ 1	$ 1
Authorized and unissued common shares reserved for issuance	150,000	150,000	150,000
Common stock, shares issued	100,693	101,179	101,403
Common stock, shares outstanding	100,693	101,179	101,403
Series A Preferred Stock [Member]
Preferred stock, shares authorized	1,000	1,000	1,000
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0