Schedule of Recorded Investment in Past Due Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Loans held for investment	$ 4,093,815		$ 4,093,815		$ 4,133,028
Mortgage loans held for sale	76,148		76,148		53,521
Total loans	4,169,963	4,281,260	4,169,963	4,281,260	4,186,549
Interest Income on Non-Accrual Loans if Accrued	584	769	1,272	1,487
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	9,570		9,570		22,124
60 to 89 Days Past Due	4,391		4,391		7,871
Greater than 90 Days Past Due	1,295		1,295		630
Total Loans 30 or More Days Past Due	15,256		15,256		30,625
Current Loans	1,450,257		1,450,257		1,455,139
Non-accrual Loans	51,887		51,887		67,391
Loans held for investment	1,517,400		1,517,400		1,553,155
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	4,064		4,064		5,251
60 to 89 Days Past Due	1,876		1,876		2,448
Greater than 90 Days Past Due	49		49		867
Total Loans 30 or More Days Past Due	5,989		5,989		8,566
Current Loans	198,950		198,950		208,134
Non-accrual Loans	35,611		35,611		61,913
Loans held for investment	240,550		240,550		278,613
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	411		411		415
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	411		411		415
Current Loans	47,609		47,609		56,219
Non-accrual Loans	3,173		3,173		4,472
Loans held for investment	51,193		51,193		61,106
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0		0		1,698
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		1,698
Current Loans	48,889		48,889		34,820
Non-accrual Loans	11,022		11,022		24,536
Loans held for investment	59,911		59,911		61,054
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	4,475		4,475		7,364
60 to 89 Days Past Due	1,876		1,876		2,448
Greater than 90 Days Past Due	49		49		867
Total Loans 30 or More Days Past Due	6,400		6,400		10,679
Current Loans	295,448		295,448		299,173
Non-accrual Loans	49,806		49,806		90,921
Loans held for investment	351,654		351,654		400,773
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	5,234		5,234		4,669
60 to 89 Days Past Due	1,264		1,264		973
Greater than 90 Days Past Due	1,231		1,231		1,798
Total Loans 30 or More Days Past Due	7,729		7,729		7,440
Current Loans	552,998		552,998		546,278
Non-accrual Loans	11,291		11,291		18,225
Loans held for investment	572,018		572,018		571,943
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	14,072		14,072		4,103
60 to 89 Days Past Due	865		865		1,831
Greater than 90 Days Past Due	0		0		0
Total Loans 30 or More Days Past Due	14,937		14,937		5,934
Current Loans	151,399		151,399		166,119
Non-accrual Loans	4,751		4,751		3,249
Loans held for investment	171,087		171,087		175,302
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	33,351		33,351		38,260
60 to 89 Days Past Due	8,396		8,396		13,123
Greater than 90 Days Past Due	2,575		2,575		3,295
Total Loans 30 or More Days Past Due	44,322		44,322		54,678
Current Loans	2,450,102		2,450,102		2,466,709
Non-accrual Loans	117,735		117,735		179,786
Loans held for investment	2,612,159		2,612,159		2,701,173
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,035		2,035		3,078
60 to 89 Days Past Due	200		200		370
Greater than 90 Days Past Due	20		20		45
Total Loans 30 or More Days Past Due	2,255		2,255		3,493
Current Loans	415,878		415,878		403,695
Non-accrual Loans	471		471		463
Loans held for investment	418,604		418,604		407,651
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,078		1,078		1,479
60 to 89 Days Past Due	102		102		436
Greater than 90 Days Past Due	135		135		60
Total Loans 30 or More Days Past Due	1,315		1,315		1,975
Current Loans	142,423		142,423		144,625
Non-accrual Loans	704		704		887
Loans held for investment	144,442		144,442		147,487
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	428		428		604
60 to 89 Days Past Due	241		241		375
Greater than 90 Days Past Due	686		686		585
Total Loans 30 or More Days Past Due	1,355		1,355		1,564
Current Loans	56,786		56,786		59,343
Non-accrual Loans	25		25		26
Loans held for investment	58,166		58,166		60,933
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	3,541		3,541		5,161
60 to 89 Days Past Due	543		543		1,181
Greater than 90 Days Past Due	841		841		690
Total Loans 30 or More Days Past Due	4,925		4,925		7,032
Current Loans	615,087		615,087		607,663
Non-accrual Loans	1,200		1,200		1,376
Loans held for investment	621,212		621,212		616,071
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	7,062		7,062		13,721
60 to 89 Days Past Due	1,382		1,382		3,464
Greater than 90 Days Past Due	3,835		3,835		405
Total Loans 30 or More Days Past Due	12,279		12,279		17,590
Current Loans	697,231		697,231		657,609
Non-accrual Loans	10,500		10,500		18,062
Loans held for investment	720,010		720,010		693,261
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	654		654		476
60 to 89 Days Past Due	144		144		215
Greater than 90 Days Past Due	380		380		110
Total Loans 30 or More Days Past Due	1,178		1,178		801
Current Loans	136,449		136,449		118,150
Non-accrual Loans	488		488		759
Loans held for investment	138,115		138,115		119,710
Other, including overdrafts
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		2
Greater than 90 Days Past Due	0		0		0
Total Loans 30 or More Days Past Due	0		0		2
Current Loans	2,319		2,319		2,811
Non-accrual Loans	0		0		0
Loans held for investment	2,319		2,319		2,813
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	44,608		44,608		57,618
60 to 89 Days Past Due	10,465		10,465		17,985
Greater than 90 Days Past Due	7,631		7,631		4,500
Total Loans 30 or More Days Past Due	62,704		62,704		80,103
Current Loans	3,901,188		3,901,188		3,852,942
Non-accrual Loans	129,923		129,923		199,983
Loans held for investment	4,093,815		4,093,815		4,133,028
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	76,148		76,148		53,521
Non-accrual Loans	0		0		0
Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	44,608		44,608		57,618
60 to 89 Days Past Due	10,465		10,465		17,985
Greater than 90 Days Past Due	7,631		7,631		4,500
Total Loans 30 or More Days Past Due	62,704		62,704		80,103
Current Loans	3,977,336		3,977,336		3,906,463
Non-accrual Loans	129,923		129,923		199,983
Total loans	$ 4,169,963		$ 4,169,963		$ 4,186,549