Schedule of Recorded Investment in Past Due Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Loans held for investment	$ 4,169,116		$ 4,157,470
Mortgage loans held for sale	55,443		66,442
Total loans	4,224,559	4,158,616	4,223,912
Interest Income on Non-Accrual Loans if Accrued	1,352	2,702
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	12,846		5,449
60 to 89 Days Past Due	865		3,163
Greater than 90 Days Past Due	0		2
Total Loans 30 or More Days Past Due	13,711		8,614
Current Loans	1,410,640		1,438,142
Non-accrual Loans	44,951		50,516
Loans held for investment	1,469,302		1,497,272
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	6,294		3,371
60 to 89 Days Past Due	62		2,121
Greater than 90 Days Past Due	0		318
Total Loans 30 or More Days Past Due	6,356		5,810
Current Loans	192,376		195,077
Non-accrual Loans	16,773		19,309
Loans held for investment	215,505		220,196
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	92		283
60 to 89 Days Past Due	0		0
Greater than 90 Days Past Due	0		0
Total Loans 30 or More Days Past Due	92		283
Current Loans	48,726		46,816
Non-accrual Loans	1,335		2,175
Loans held for investment	50,153		49,274
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,173		0
60 to 89 Days Past Due	0		0
Greater than 90 Days Past Due	0		0
Total Loans 30 or More Days Past Due	2,173		0
Current Loans	56,572		56,933
Non-accrual Loans	6,483		8,126
Loans held for investment	65,228		65,059
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	8,559		3,654
60 to 89 Days Past Due	62		2,121
Greater than 90 Days Past Due	0		318
Total Loans 30 or More Days Past Due	8,621		6,093
Current Loans	297,674		298,826
Non-accrual Loans	24,591		29,610
Loans held for investment	330,886		334,529
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	4,269		3,896
60 to 89 Days Past Due	502		969
Greater than 90 Days Past Due	1,044		1,085
Total Loans 30 or More Days Past Due	5,815		5,950
Current Loans	744,108		691,963
Non-accrual Loans	8,557		10,426
Loans held for investment	758,480		708,339
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,464		1,187
60 to 89 Days Past Due	349		0
Greater than 90 Days Past Due	2		218
Total Loans 30 or More Days Past Due	1,815		1,405
Current Loans	166,116		171,009
Non-accrual Loans	4,591		4,830
Loans held for investment	172,522		177,244
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	27,138		14,186
60 to 89 Days Past Due	1,778		6,253
Greater than 90 Days Past Due	1,046		1,623
Total Loans 30 or More Days Past Due	29,962		22,062
Current Loans	2,618,538		2,599,940
Non-accrual Loans	82,690		95,382
Loans held for investment	2,731,190		2,717,384
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,166		3,218
60 to 89 Days Past Due	326		512
Greater than 90 Days Past Due	3		32
Total Loans 30 or More Days Past Due	2,495		3,762
Current Loans	441,477		434,200
Non-accrual Loans	285		283
Loans held for investment	444,257		438,245
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	642		1,044
60 to 89 Days Past Due	157		104
Greater than 90 Days Past Due	1		31
Total Loans 30 or More Days Past Due	800		1,179
Current Loans	133,786		135,574
Non-accrual Loans	888		990
Loans held for investment	135,474		137,743
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	308		409
60 to 89 Days Past Due	222		278
Greater than 90 Days Past Due	467		392
Total Loans 30 or More Days Past Due	997		1,079
Current Loans	55,614		59,704
Non-accrual Loans	22		23
Loans held for investment	56,633		60,806
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	3,116		4,671
60 to 89 Days Past Due	705		894
Greater than 90 Days Past Due	471		455
Total Loans 30 or More Days Past Due	4,292		6,020
Current Loans	630,877		629,478
Non-accrual Loans	1,195		1,296
Loans held for investment	636,364		636,794
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	4,097		5,463
60 to 89 Days Past Due	3,966		1,064
Greater than 90 Days Past Due	329		216
Total Loans 30 or More Days Past Due	8,392		6,743
Current Loans	665,884		671,414
Non-accrual Loans	14,568		10,596
Loans held for investment	688,844		688,753
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	813		1,710
60 to 89 Days Past Due	311		361
Greater than 90 Days Past Due	95		0
Total Loans 30 or More Days Past Due	1,219		2,071
Current Loans	110,051		111,031
Non-accrual Loans	141		525
Loans held for investment	111,411		113,627
Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due			0
60 to 89 Days Past Due	0		0
Greater than 90 Days Past Due	0		0
Total Loans 30 or More Days Past Due	0		0
Current Loans	1,307		912
Non-accrual Loans	0		0
Loans held for investment	1,307		912
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	35,164		26,030
60 to 89 Days Past Due	6,760		8,572
Greater than 90 Days Past Due	1,941		2,294
Total Loans 30 or More Days Past Due	43,865		36,896
Current Loans	4,026,657		4,012,775
Non-accrual Loans	98,594		107,799
Loans held for investment	4,169,116		4,157,470
Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0		0
60 to 89 Days Past Due	0		0
Greater than 90 Days Past Due	0		0
Total Loans 30 or More Days Past Due	0		0
Current Loans	55,443		66,442
Non-accrual Loans	0		0
Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	35,164		26,030
60 to 89 Days Past Due	6,760		8,572
Greater than 90 Days Past Due	1,941		2,294
Total Loans 30 or More Days Past Due	43,865		36,896
Current Loans	4,082,100		4,079,217
Non-accrual Loans	98,594		107,799
Total loans	$ 4,224,559		$ 4,223,912