Schedule of Recorded Investment in Past Due Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Loans held for investment	$ 4,223,078		$ 4,157,470
Mortgage loans held for sale	74,286		66,442
Total loans	4,297,364	4,169,963	4,223,912
Interest Income on Non-Accrual Loans if Accrued	318	584
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	11,794		5,449
60 to 89 Days Past Due	1,766		3,163
Greater than 90 Days Past Due	0		2
Total Loans 30 or More Days Past Due	13,560		8,614
Current Loans	1,387,523		1,438,142
Non-accrual Loans	46,062		50,516
Loans held for investment	1,447,145		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	4,265		3,371
60 to 89 Days Past Due	974		2,121
Greater than 90 Days Past Due	61		318
Total Loans 30 or More Days Past Due	5,300		5,810
Current Loans	189,173		195,077
Non-accrual Loans	16,288		19,309
Loans held for investment	210,761		220,196
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,112		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	1,112		283
Current Loans	58,245		46,816
Non-accrual Loans	1,526		2,175
Loans held for investment	60,883		49,274
Commercial construction real estate
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	59,375		56,933
Non-accrual Loans	6,192		8,126
Loans held for investment	65,567		65,059
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	5,377		3,654
60 to 89 Days Past Due	974		2,121
Greater than 90 Days Past Due	61		318
Total Loans 30 or More Days Past Due	6,412		6,093
Current Loans	306,793		298,826
Non-accrual Loans	24,006		29,610
Loans held for investment	337,211		334,529
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,139		3,896
60 to 89 Days Past Due	1,033		969
Greater than 90 Days Past Due	701		1,085
Total Loans 30 or More Days Past Due	3,873		5,950
Current Loans	792,782		691,963
Non-accrual Loans	7,545		10,426
Loans held for investment	804,200		708,339
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	350		1,187
60 to 89 Days Past Due	0		0
Greater than 90 Days Past Due	83		218
Total Loans 30 or More Days Past Due	433		1,405
Current Loans	166,677		171,009
Non-accrual Loans	9,689		4,830
Loans held for investment	176,799		177,244
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	19,660		14,186
60 to 89 Days Past Due	3,773		6,253
Greater than 90 Days Past Due	845		1,623
Total Loans 30 or More Days Past Due	24,278		22,062
Current Loans	2,653,775		2,599,940
Non-accrual Loans	87,302		95,382
Loans held for investment	2,765,355		2,717,384
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,006		3,218
60 to 89 Days Past Due	416		512
Greater than 90 Days Past Due	38		32
Total Loans 30 or More Days Past Due	2,460		3,762
Current Loans	454,395		434,200
Non-accrual Loans	296		283
Loans held for investment	457,151		438,245
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	867		1,044
60 to 89 Days Past Due	63		104
Greater than 90 Days Past Due	14		31
Total Loans 30 or More Days Past Due	944		1,179
Current Loans	134,975		135,574
Non-accrual Loans	540		990
Loans held for investment	136,459		137,743
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	301		409
60 to 89 Days Past Due	275		278
Greater than 90 Days Past Due	487		392
Total Loans 30 or More Days Past Due	1,063		1,079
Current Loans	58,250		59,704
Non-accrual Loans	21		23
Loans held for investment	59,334		60,806
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	3,174		4,671
60 to 89 Days Past Due	754		894
Greater than 90 Days Past Due	539		455
Total Loans 30 or More Days Past Due	4,467		6,020
Current Loans	647,620		629,478
Non-accrual Loans	857		1,296
Loans held for investment	652,944		636,794
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	8,235		5,463
60 to 89 Days Past Due	1,523		1,064
Greater than 90 Days Past Due	361		216
Total Loans 30 or More Days Past Due	10,119		6,743
Current Loans	655,189		671,414
Non-accrual Loans	15,443		10,596
Loans held for investment	680,751		688,753
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,264		1,710
60 to 89 Days Past Due	1,025		361
Greater than 90 Days Past Due	0		0
Total Loans 30 or More Days Past Due	2,289		2,071
Current Loans	119,114		111,031
Non-accrual Loans	127		525
Loans held for investment	121,530		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	2,498		912
Non-accrual Loans	0		0
Loans held for investment	2,498		912
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	32,333		26,030
60 to 89 Days Past Due	7,075		8,572
Greater than 90 Days Past Due	1,745		2,294
Total Loans 30 or More Days Past Due	41,153		36,896
Current Loans	4,078,196		4,012,775
Non-accrual Loans	103,729		107,799
Loans held for investment	4,223,078		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	74,286		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	32,333		26,030
60 to 89 Days Past Due	7,075		8,572
Greater than 90 Days Past Due	1,745		2,294
Total Loans 30 or More Days Past Due	41,153		36,896
Current Loans	4,152,482		4,079,217
Non-accrual Loans	103,729		107,799
Total loans	$ 4,297,364		$ 4,223,912