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, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Loans held for investment	$ 4,107,171		$ 4,107,171		$ 4,133,028
Mortgage loans held for sale	72,880		72,880		53,521
Total loans	4,180,051	4,275,717	4,180,051	4,275,717	4,186,549
Interest Income on Non-Accrual Loans if Accrued	456	819	1,701	2,283
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	15,120		15,120		22,124
60 to 89 Days Past Due	3,061		3,061		7,871
Greater than 90 Days Past Due	643		643		630
Total Loans 30 or More Days Past Due	18,824		18,824		30,625
Current Loans	1,443,893		1,443,893		1,455,139
Non-accrual Loans	51,067		51,067		67,391
Loans held for investment	1,513,784		1,513,784		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	3,518		3,518		5,251
60 to 89 Days Past Due	326		326		2,448
Greater than 90 Days Past Due	0		0		867
Total Loans 30 or More Days Past Due	3,844		3,844		8,566
Current Loans	199,991		199,991		208,134
Non-accrual Loans	29,247		29,247		61,913
Loans held for investment	233,082		233,082		278,613
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,049		1,049		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	1,049		1,049		415
Current Loans	47,077		47,077		56,219
Non-accrual Loans	2,769		2,769		4,472
Loans held for investment	50,895		50,895		61,106
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,875		1,875		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	1,875		1,875		1,698
Current Loans	43,703		43,703		34,820
Non-accrual Loans	10,519		10,519		24,536
Loans held for investment	56,097		56,097		61,054
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	6,442		6,442		7,364
60 to 89 Days Past Due	326		326		2,448
Greater than 90 Days Past Due	0		0		867
Total Loans 30 or More Days Past Due	6,768		6,768		10,679
Current Loans	290,771		290,771		299,173
Non-accrual Loans	42,535		42,535		90,921
Loans held for investment	340,074		340,074		400,773
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	3,674		3,674		4,669
60 to 89 Days Past Due	1,064		1,064		973
Greater than 90 Days Past Due	2,382		2,382		1,798
Total Loans 30 or More Days Past Due	7,120		7,120		7,440
Current Loans	621,601		621,601		546,278
Non-accrual Loans	10,514		10,514		18,225
Loans held for investment	639,235		639,235		571,943
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	6,419		6,419		4,103
60 to 89 Days Past Due	22		22		1,831
Greater than 90 Days Past Due	217		217		0
Total Loans 30 or More Days Past Due	6,658		6,658		5,934
Current Loans	163,943		163,943		166,119
Non-accrual Loans	4,794		4,794		3,249
Loans held for investment	175,395		175,395		175,302
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	31,655		31,655		38,260
60 to 89 Days Past Due	4,473		4,473		13,123
Greater than 90 Days Past Due	3,242		3,242		3,295
Total Loans 30 or More Days Past Due	39,370		39,370		54,678
Current Loans	2,520,208		2,520,208		2,466,709
Non-accrual Loans	108,910		108,910		179,786
Loans held for investment	2,668,488		2,668,488		2,701,173
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,792		2,792		3,078
60 to 89 Days Past Due	385		385		370
Greater than 90 Days Past Due	47		47		45
Total Loans 30 or More Days Past Due	3,224		3,224		3,493
Current Loans	427,774		427,774		403,695
Non-accrual Loans	451		451		463
Loans held for investment	431,449		431,449		407,651
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	822		822		1,479
60 to 89 Days Past Due	129		129		436
Greater than 90 Days Past Due	24		24		60
Total Loans 30 or More Days Past Due	975		975		1,975
Current Loans	137,904		137,904		144,625
Non-accrual Loans	1,105		1,105		887
Loans held for investment	139,984		139,984		147,487
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	368		368		604
60 to 89 Days Past Due	280		280		375
Greater than 90 Days Past Due	528		528		585
Total Loans 30 or More Days Past Due	1,176		1,176		1,564
Current Loans	57,125		57,125		59,343
Non-accrual Loans	23		23		26
Loans held for investment	58,324		58,324		60,933
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	3,982		3,982		5,161
60 to 89 Days Past Due	794		794		1,181
Greater than 90 Days Past Due	599		599		690
Total Loans 30 or More Days Past Due	5,375		5,375		7,032
Current Loans	622,803		622,803		607,663
Non-accrual Loans	1,579		1,579		1,376
Loans held for investment	629,757		629,757		616,071
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	5,185		5,185		13,721
60 to 89 Days Past Due	1,808		1,808		3,464
Greater than 90 Days Past Due	823		823		405
Total Loans 30 or More Days Past Due	7,816		7,816		17,590
Current Loans	652,420		652,420		657,609
Non-accrual Loans	11,864		11,864		18,062
Loans held for investment	672,100		672,100		693,261
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	234		234		476
60 to 89 Days Past Due	146		146		215
Greater than 90 Days Past Due	0		0		110
Total Loans 30 or More Days Past Due	380		380		801
Current Loans	134,509		134,509		118,150
Non-accrual Loans	578		578		759
Loans held for investment	135,467		135,467		119,710
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					2
Greater than 90 Days Past Due					0
Total Loans 30 or More Days Past Due	0		0		2
Current Loans	1,359		1,359		2,811
Non-accrual Loans	0		0		0
Loans held for investment	1,359		1,359		2,813
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	41,056		41,056		57,618
60 to 89 Days Past Due	7,221		7,221		17,985
Greater than 90 Days Past Due	4,664		4,664		4,500
Total Loans 30 or More Days Past Due	52,941		52,941		80,103
Current Loans	3,931,299		3,931,299		3,852,942
Non-accrual Loans	122,931		122,931		199,983
Loans held for investment	4,107,171		4,107,171		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	72,880		72,880		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	41,056		41,056		57,618
60 to 89 Days Past Due	7,221		7,221		17,985
Greater than 90 Days Past Due	4,664		4,664		4,500
Total Loans 30 or More Days Past Due	52,941		52,941		80,103
Current Loans	4,004,179		4,004,179		3,906,463
Non-accrual Loans	122,931		122,931		199,983
Total loans	$ 4,180,051		$ 4,180,051		$ 4,186,549