Loans - Schedule of Recorded Investment in Impaired Loans (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	$ 158,512	$ 264,801	$ 212,877
Recorded Investment With No Allowance	82,232	117,004	76,672
Recorded Investment With Allowance	53,953	113,592	122,630
Total Recorded Investment	136,185	230,596	199,302
Related allowance	10,297	32,838	42,226
Commercial real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	84,300	97,745	79,193
Recorded Investment With No Allowance	39,049	62,769	31,925
Recorded Investment With Allowance	34,774	23,218	41,703
Total Recorded Investment	73,823	85,987	73,628
Related allowance	4,112	6,741	10,315
Land acquisition & development construction real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	28,558	73,258	48,371
Recorded Investment With No Allowance	15,891	22,300	24,120
Recorded Investment With Allowance	7,173	39,131	20,440
Total Recorded Investment	23,064	61,431	44,560
Related allowance	1,457	12,084	8,064
Residential construction real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	3,018	13,721	18,632
Recorded Investment With No Allowance	1,976	10,427	2,993
Recorded Investment With Allowance	710	2,044	13,721
Total Recorded Investment	2,686	12,471	16,714
Related allowance	251	312	3,431
Commercial construction real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	10,447	26,647	17,458
Recorded Investment With No Allowance	7,785	3,510	2,976
Recorded Investment With Allowance	340	21,026	13,578
Total Recorded Investment	8,125	24,536	16,554
Related allowance	69	5,042	3,877
Total construction loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	42,023	113,626	84,461
Recorded Investment With No Allowance	25,652	36,237	30,089
Recorded Investment With Allowance	8,223	62,201	47,739
Total Recorded Investment	33,875	98,438	77,828
Related allowance	1,777	17,438	15,372
Residential real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	13,271	18,305	8,951
Recorded Investment With No Allowance	6,152	2,678	1,741
Recorded Investment With Allowance	4,495	15,626	7,110
Total Recorded Investment	10,647	18,304	8,851
Related allowance	1,677	3,844	1,266
Agricultural real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	5,559	8,018	3,045
Recorded Investment With No Allowance	1,834	7,470	1,065
Recorded Investment With Allowance	3,227	0	1,432
Total Recorded Investment	5,061	7,470	2,497
Related allowance	784	0	128
Total real estate loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	145,153	237,694	175,650
Recorded Investment With No Allowance	72,687	109,154	64,820
Recorded Investment With Allowance	50,719	101,045	97,984
Total Recorded Investment	123,406	210,199	162,804
Related allowance	8,350	28,023	27,081
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	12,770	26,348	36,251
Recorded Investment With No Allowance	9,036	7,354	11,354
Recorded Investment With Allowance	3,206	12,284	24,168
Total Recorded Investment	12,242	19,638	35,522
Related allowance	1,919	4,664	14,892
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	589	759	976
Recorded Investment With No Allowance	509	496	498
Recorded Investment With Allowance	28	263	478
Total Recorded Investment	537	759	976
Related allowance	$ 28	$ 151	$ 253