Allowance for Probable Loan Losses (Details 4) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Interest Recognized
Loans accounted for as troubled debt restructuring	$ 20,275,000		$ 20,275,000		$ 29,395,000
Period of charge off for past due unsecured commercial loans			90 days
Class of financing receivable
Recorded investment:
Total impaired loans with related allowance	32,450,000		32,450,000		11,982,000
Total impaired loans with no related allowance	66,576,000		66,576,000		71,023,000
Unpaid principal balance:
Total impaired loans with an allowance recorded	35,838,000		35,838,000		15,273,000
Total impaired loans with no related allowance recorded	68,436,000		68,436,000		73,728,000
Related Allowance	14,997,000		14,997,000		4,746,000
Average recorded investment:
Total impaired loans with an allowance recorded	32,476,000	33,715,000	30,736,000	57,716,000	35,076,000
Total impaired loans with no related allowance recorded	58,267,000	48,128,000	53,089,000	49,061,000	65,536,000
Interest Recognized
Total impaired loans with an allowance recorded	32,000	33,000	98,000	98,000	131,000
Total impaired loans with no related allowance recorded	92,000	64,000	258,000	244,000	323,000
Commercial | Class of financing receivable
Recorded investment:
Total impaired loans with related allowance	17,880,000		17,880,000		1,633,000
Total impaired loans with no related allowance	17,351,000		17,351,000		31,135,000
Unpaid principal balance:
Total impaired loans with an allowance recorded	17,880,000		17,880,000		1,679,000
Total impaired loans with no related allowance recorded	17,993,000		17,993,000		31,170,000
Related Allowance	10,741,000		10,741,000		1,477,000
Average recorded investment:
Total impaired loans with an allowance recorded	17,884,000	22,729,000	17,898,000	22,517,000	21,126,000
Total impaired loans with no related allowance recorded	17,238,000	840,000	16,915,000	538,000	2,996,000
Interest Recognized
Total impaired loans with an allowance recorded	9,000	10,000	29,000	29,000	39,000
Total impaired loans with no related allowance recorded		1,000		3,000	4,000
Commercial real estate: other construction and land development | Class of financing receivable
Recorded investment:
Total impaired loans with related allowance	6,819,000		6,819,000		3,671,000
Total impaired loans with no related allowance	29,485,000		29,485,000		24,989,000
Unpaid principal balance:
Total impaired loans with an allowance recorded	6,825,000		6,825,000		3,671,000
Total impaired loans with no related allowance recorded	29,542,000		29,542,000		25,160,000
Related Allowance	852,000		852,000		539,000
Average recorded investment:
Total impaired loans with an allowance recorded	6,821,000	3,671,000	5,804,000	23,479,000	6,608,000
Total impaired loans with no related allowance recorded	22,414,000	26,689,000	20,788,000	27,632,000	39,449,000
Interest Recognized
Total impaired loans with no related allowance recorded	17,000	23,000	53,000	122,000	141,000
Commercial real estate: farmland and commercial | Class of financing receivable
Recorded investment:
Total impaired loans with related allowance	7,751,000		7,751,000		6,678,000
Total impaired loans with no related allowance	9,287,000		9,287,000		7,267,000
Unpaid principal balance:
Total impaired loans with an allowance recorded	11,133,000		11,133,000		9,923,000
Total impaired loans with no related allowance recorded	10,289,000		10,289,000		9,340,000
Related Allowance	3,404,000		3,404,000		2,730,000
Average recorded investment:
Total impaired loans with an allowance recorded	7,771,000	7,117,000	7,034,000	11,518,000	7,342,000
Total impaired loans with no related allowance recorded	8,775,000	14,069,000	6,787,000	14,850,000	16,536,000
Interest Recognized
Total impaired loans with an allowance recorded	23,000	23,000	69,000	69,000	92,000
Total impaired loans with no related allowance recorded				8,000	8,000
Commercial real estate: multifamily | Class of financing receivable
Recorded investment:
Total impaired loans with no related allowance	314,000		314,000		353,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded	314,000		314,000		353,000
Average recorded investment:
Total impaired loans with no related allowance recorded	316,000	374,000	330,000	388,000	381,000
Residential: first lien | Class of financing receivable
Recorded investment:
Total impaired loans with no related allowance	4,984,000		4,984,000		3,656,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded	5,117,000		5,117,000		3,984,000
Average recorded investment:
Total impaired loans with an allowance recorded		198,000		202,000
Total impaired loans with no related allowance recorded	4,878,000	2,957,000	4,441,000	2,485,000	2,876,000
Interest Recognized
Total impaired loans with no related allowance recorded	45,000	15,000	117,000	31,000	60,000
Residential: junior lien | Class of financing receivable
Recorded investment:
Total impaired loans with no related allowance	3,219,000		3,219,000		1,850,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded	3,238,000		3,238,000		1,944,000
Average recorded investment:
Total impaired loans with no related allowance recorded	2,731,000	1,836,000	2,059,000	1,958,000	1,939,000
Interest Recognized
Total impaired loans with no related allowance recorded	25,000	25,000	74,000	79,000	104,000
Consumer | Class of financing receivable
Recorded investment:
Total impaired loans with no related allowance	1,481,000		1,481,000		1,326,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded	1,486,000		1,486,000		1,330,000
Average recorded investment:
Total impaired loans with no related allowance recorded	1,458,000	1,271,000	1,313,000	1,149,000	1,193,000
Foreign | Class of financing receivable
Recorded investment:
Total impaired loans with no related allowance	455,000		455,000		447,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded	457,000		457,000		447,000
Average recorded investment:
Total impaired loans with no related allowance recorded	457,000	92,000	456,000	61,000	166,000
Interest Recognized
Total impaired loans with no related allowance recorded	$ 5,000		$ 14,000	$ 1,000	$ 6,000