Schedule of Recorded Investment in Past Due Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Loans held for investment	$ 4,279,959		$ 4,279,959		$ 4,157,470
Mortgage loans held for sale	52,133		52,133		66,442
Total loans	4,332,092	4,180,051	4,332,092	4,180,051	4,223,912
Interest Income on Non-Accrual Loans if Accrued	1,216	1,821	3,877	6,844
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	4,333		4,333		5,449
60 to 89 Days Past Due	4,124		4,124		3,163
Greater than 90 Days Past Due	313		313		2
Total Loans 30 or More Days Past Due	8,770		8,770		8,614
Current Loans	1,386,656		1,386,656		1,438,142
Non-accrual Loans	45,871		45,871		50,516
Loans held for investment	1,441,297		1,441,297		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	6,652		6,652		3,371
60 to 89 Days Past Due	925		925		2,121
Greater than 90 Days Past Due	0		0		318
Total Loans 30 or More Days Past Due	7,577		7,577		5,810
Current Loans	185,841		185,841		195,077
Non-accrual Loans	16,735		16,735		19,309
Loans held for investment	210,153		210,153		220,196
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	41		41		283
60 to 89 Days Past Due	0		0		0
Greater than 90 Days Past Due	0		0		0
Total Loans 30 or More Days Past Due	41		41		283
Current Loans	66,831		66,831		46,816
Non-accrual Loans	1,490		1,490		2,175
Loans held for investment	68,362		68,362		49,274
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,207		2,207		0
60 to 89 Days Past Due	0		0		0
Greater than 90 Days Past Due	0		0		0
Total Loans 30 or More Days Past Due	2,207		2,207		0
Current Loans	60,294		60,294		56,933
Non-accrual Loans	268		268		8,126
Loans held for investment	62,769		62,769		65,059
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	8,900		8,900		3,654
60 to 89 Days Past Due	925		925		2,121
Greater than 90 Days Past Due	0		0		318
Total Loans 30 or More Days Past Due	9,825		9,825		6,093
Current Loans	312,966		312,966		298,826
Non-accrual Loans	18,493		18,493		29,610
Loans held for investment	341,284		341,284		334,529
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,970		2,970		3,896
60 to 89 Days Past Due	996		996		969
Greater than 90 Days Past Due	875		875		1,085
Total Loans 30 or More Days Past Due	4,841		4,841		5,950
Current Loans	830,616		830,616		691,963
Non-accrual Loans	6,250		6,250		10,426
Loans held for investment	841,707		841,707		708,339
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	272		272		1,187
60 to 89 Days Past Due	4,949		4,949		0
Greater than 90 Days Past Due	48		48		218
Total Loans 30 or More Days Past Due	5,269		5,269		1,405
Current Loans	161,544		161,544		171,009
Non-accrual Loans	9,781		9,781		4,830
Loans held for investment	176,594		176,594		177,244
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	16,475		16,475		14,186
60 to 89 Days Past Due	10,994		10,994		6,253
Greater than 90 Days Past Due	1,236		1,236		1,623
Total Loans 30 or More Days Past Due	28,705		28,705		22,062
Current Loans	2,691,782		2,691,782		2,599,940
Non-accrual Loans	80,395		80,395		95,382
Loans held for investment	2,800,882		2,800,882		2,717,384
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,343		2,343		3,218
60 to 89 Days Past Due	244		244		512
Greater than 90 Days Past Due	0		0		32
Total Loans 30 or More Days Past Due	2,587		2,587		3,762
Current Loans	473,611		473,611		434,200
Non-accrual Loans	333		333		283
Loans held for investment	476,531		476,531		438,245
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	798		798		1,044
60 to 89 Days Past Due	117		117		104
Greater than 90 Days Past Due	3		3		31
Total Loans 30 or More Days Past Due	918		918		1,179
Current Loans	134,179		134,179		135,574
Non-accrual Loans	541		541		990
Loans held for investment	135,638		135,638		137,743
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	364		364		409
60 to 89 Days Past Due	262		262		278
Greater than 90 Days Past Due	469		469		392
Total Loans 30 or More Days Past Due	1,095		1,095		1,079
Current Loans	58,900		58,900		59,704
Non-accrual Loans	20		20		23
Loans held for investment	60,015		60,015		60,806
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	3,505		3,505		4,671
60 to 89 Days Past Due	623		623		894
Greater than 90 Days Past Due	472		472		455
Total Loans 30 or More Days Past Due	4,600		4,600		6,020
Current Loans	666,690		666,690		629,478
Non-accrual Loans	894		894		1,296
Loans held for investment	672,184		672,184		636,794
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	6,102		6,102		5,463
60 to 89 Days Past Due	1,159		1,159		1,064
Greater than 90 Days Past Due	534		534		216
Total Loans 30 or More Days Past Due	7,795		7,795		6,743
Current Loans	661,010		661,010		671,414
Non-accrual Loans	12,611		12,611		10,596
Loans held for investment	681,416		681,416		688,753
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	520		520		1,710
60 to 89 Days Past Due	36		36		361
Greater than 90 Days Past Due	0		0		0
Total Loans 30 or More Days Past Due	556		556		2,071
Current Loans	122,894		122,894		111,031
Non-accrual Loans	115		115		525
Loans held for investment	123,565		123,565		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		0
Greater than 90 Days Past Due	0		0		0
Total Loans 30 or More Days Past Due	0		0		0
Current Loans	1,912		1,912		912
Non-accrual Loans	0		0		0
Loans held for investment	1,912		1,912		912
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	26,602		26,602		26,030
60 to 89 Days Past Due	12,812		12,812		8,572
Greater than 90 Days Past Due	2,242		2,242		2,294
Total Loans 30 or More Days Past Due	41,656		41,656		36,896
Current Loans	4,144,288		4,144,288		4,012,775
Non-accrual Loans	94,015		94,015		107,799
Loans held for investment	4,279,959		4,279,959		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		0
60 to 89 Days Past Due	0		0		0
Greater than 90 Days Past Due	0		0		0
Total Loans 30 or More Days Past Due	0		0		0
Current Loans	52,133		52,133		66,442
Non-accrual Loans	0		0		0
Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	26,602		26,602		26,030
60 to 89 Days Past Due	12,812		12,812		8,572
Greater than 90 Days Past Due	2,242		2,242		2,294
Total Loans 30 or More Days Past Due	41,656		41,656		36,896
Current Loans	4,196,421		4,196,421		4,079,217
Non-accrual Loans	94,015		94,015		107,799
Total loans	$ 4,332,092		$ 4,332,092		$ 4,223,912