Loans and Allowance for Credit Losses (Details 7) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Allowance for credit losses
Beginning balance	$ 60,732	$ 76,792	$ 61,234	$ 71,229
Charge-offs	(3,749)	(11,194)	(8,741)	(19,802)
Recoveries	396	456	1,099	810
Provision	4,297	9,112	8,084	22,929
Ending balance	61,676	75,166	61,676	75,166
Ending balance: individually evaluated for impairment	11,734	34,866	11,734	34,866
Ending balance: collectively evaluated for impairment	49,942	40,300	49,942	40,300
Ending balance	4,159,531	3,992,058	4,159,531	3,992,058	4,043,643
Ending balance: individually evaluated for impairment	80,590	143,451	80,590	143,451
Ending balance: collectively evaluated for impairment	4,078,941	3,848,607	4,078,941	3,848,607
Commercial, Financial, Agricultural and Other [Member]
Allowance for credit losses
Beginning balance	18,143	22,436	18,200	21,700
Charge-offs	(1,754)	(1,997)	(3,668)	(2,957)
Recoveries	37	157	275	261
Provision	2,876	2,579	4,495	4,171
Ending balance	19,302	23,175	19,302	23,175
Ending balance: individually evaluated for impairment	8,046	12,717	8,046	12,717
Ending balance: collectively evaluated for impairment	11,256	10,458	11,256	10,458
Ending balance	1,059,675	943,186	1,059,675	943,186
Ending balance: individually evaluated for impairment	31,271	40,447	31,271	40,447
Ending balance: collectively evaluated for impairment	1,028,404	902,739	1,028,404	902,739
Real Estate Construction [Member]
Allowance for credit losses
Beginning balance	6,427	18,779	6,756	18,002
Charge-offs	(150)	(3,049)	(340)	(8,048)
Recoveries	36	0	92	0
Provision	1,688	1,971	1,493	7,747
Ending balance	8,001	17,701	8,001	17,701
Ending balance: individually evaluated for impairment	2,747	14,222	2,747	14,222
Ending balance: collectively evaluated for impairment	5,254	3,479	5,254	3,479
Ending balance	77,442	146,113	77,442	146,113
Ending balance: individually evaluated for impairment	14,915	37,087	14,915	37,087
Ending balance: collectively evaluated for impairment	62,527	109,026	62,527	109,026
Residential Real Estate [Member]
Allowance for credit losses
Beginning balance	6,702	6,682	8,237	5,454
Charge-offs	(742)	(596)	(2,454)	(1,700)
Recoveries	149	77	282	96
Provision	510	707	554	3,020
Ending balance	6,619	6,870	6,619	6,870
Ending balance: individually evaluated for impairment	431	216	431	216
Ending balance: collectively evaluated for impairment	6,188	6,654	6,188	6,654
Ending balance	1,213,610	1,101,859	1,213,610	1,101,859
Ending balance: individually evaluated for impairment	2,911	2,174	2,911	2,174
Ending balance: collectively evaluated for impairment	1,210,699	1,099,685	1,210,699	1,099,685
Commercial Real Estate Portfolio Segment [Member]
Allowance for credit losses
Beginning balance	19,371	20,174	18,961	16,913
Charge-offs	(306)	(4,809)	(541)	(5,575)
Recoveries	28	88	186	164
Provision	(1,455)	3,327	(968)	7,278
Ending balance	17,638	18,780	17,638	18,780
Ending balance: individually evaluated for impairment	510	7,711	510	7,711
Ending balance: collectively evaluated for impairment	17,128	11,069	17,128	11,069
Ending balance	1,232,270	1,270,797	1,232,270	1,270,797
Ending balance: individually evaluated for impairment	31,493	63,743	31,493	63,743
Ending balance: collectively evaluated for impairment	1,200,777	1,207,054	1,200,777	1,207,054
Loans to Individuals [Member]
Allowance for credit losses
Beginning balance	4,252	3,861	4,244	4,215
Charge-offs	(797)	(743)	(1,738)	(1,522)
Recoveries	146	134	264	289
Provision	608	618	1,439	888
Ending balance	4,209	3,870	4,209	3,870
Ending balance: individually evaluated for impairment	0	0	0	0
Ending balance: collectively evaluated for impairment	4,209	3,870	4,209	3,870
Ending balance	576,534	530,103	576,534	530,103
Ending balance: individually evaluated for impairment	0	0	0	0
Ending balance: collectively evaluated for impairment	576,534	530,103	576,534	530,103
Unallocated [Member]
Allowance for credit losses
Beginning balance	5,837	4,860	4,836	4,945
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	70	(90)	1,071	(175)
Ending balance	5,907	4,770	5,907	4,770
Ending balance: individually evaluated for impairment	0	0	0	0
Ending balance: collectively evaluated for impairment	$ 5,907	$ 4,770	$ 5,907	$ 4,770