Allowance for Probable Loan Losses (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Loan loss allowances, impaired financing receivable
Period of charge off for past due unsecured commercial loans (in days)			90
Loans with Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	$ 36,945		$ 36,945		$ 87,369
Unpaid Principal Balance	40,082		40,082		87,419
Related Allowance	18,631		18,631		27,252
Average Recorded Investment	64,403	73,545	71,543	79,390	87,951
Interest Recognized	23	357	56	761	858
Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	41,321		41,321		48,936
Unpaid Principal Balance	41,955		41,955		51,423
Average Recorded Investment	51,563	35,727	53,908	43,663	54,359
Interest Recognized	81	79	179	116	399
Commercial | Loans with Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	24,256		24,256		24,108
Unpaid Principal Balance	24,256		24,256		24,108
Related Allowance	15,098		15,098		14,402
Average Recorded Investment	24,271	22,944	24,417	22,948	24,145
Interest Recognized		10	10	20	41
Commercial | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	3,797		3,797		3,495
Unpaid Principal Balance	3,908		3,908		3,932
Average Recorded Investment	3,798	439	3,808	458	3,942
Interest Recognized	1	4	1	9	20
Commercial real estate: other construction and land development | Loans with Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	3,671		3,671		34,417
Unpaid Principal Balance	3,671		3,671		34,432
Related Allowance	568		568		3,073
Average Recorded Investment	27,377	27,815	33,384	32,873	34,709
Interest Recognized		140		328
Commercial real estate: other construction and land development | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	22,045		22,045		26,011
Unpaid Principal Balance	22,110		22,110		26,112
Average Recorded Investment	29,816	24,637	31,627	28,473	27,722
Interest Recognized	41	24	99	56	128
Commercial real estate: farmland and commercial | Loans with Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	8,817		8,817		28,636
Unpaid Principal Balance	11,954		11,954		28,671
Related Allowance	2,942		2,942		9,754
Average Recorded Investment	12,553	22,267	13,539	22,231	28,883
Interest Recognized	23	207	46	413	817
Commercial real estate: farmland and commercial | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	9,511		9,511		13,595
Unpaid Principal Balance	9,854		9,854		15,394
Average Recorded Investment	11,545	5,501	11,996	4,783	16,271
Interest Recognized			8		102
Commercial real estate: multifamily | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	382		382		411
Unpaid Principal Balance	382		382		411
Average Recorded Investment	387	445	394	454	439
Residential: first lien | Loans with Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	201		201		208
Unpaid Principal Balance	201		201		208
Related Allowance	23		23		23
Average Recorded Investment	202	519	203	1,338	214
Residential: first lien | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	2,551		2,551		2,082
Unpaid Principal Balance	2,588		2,588		2,220
Average Recorded Investment	2,681	1,944	2,596	2,000	2,230
Interest Recognized	11	3	16	3	27
Residential: junior lien | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	1,910		1,910		1,962
Unpaid Principal Balance	1,987		1,987		1,970
Average Recorded Investment	2,113	1,531	2,119	1,535	1,980
Interest Recognized	27	48	54	48	118
Consumer | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	1,080		1,080		1,334
Unpaid Principal Balance	1,081		1,081		1,338
Average Recorded Investment	1,178	1,228	1,323	1,372	1,729
Foreign | Loans with No Related Allowance
Loan loss allowances, impaired financing receivable
Recorded Investment	45		45		46
Unpaid Principal Balance	45		45		46
Average Recorded Investment	45	2	45	3	46
Interest Recognized	$ 1		$ 1		$ 4