Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Investment securities - held-to-maturity, fair value	$ 419,326	$ 433,201	$ 493,704
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	100,881	101,179	94,687
Common stock, shares outstanding	100,881	101,179	94,687
Series A Preferred Stock [Member]
Preferred stock, shares authorized	1,000	1,000	1,000
Preferred stock, shares sold	0	0	0
Preferred stock, shares outstanding	0	0	0