Loans - Schedule of Recorded Investment in Past Due Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loans and Leases Receivable Recorded Investment, Past Due
Loans held for investment	$ 4,856,615	$ 4,303,992
Mortgage loans held for sale	40,828	40,861
Total loans	4,897,443	4,344,853
Interest Income on Non-Accrual Loans if Accrued	3,970	4,630	8,537
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	4,692	5,924
60 to 89 Days Past Due	1,609	2,472
Greater than 90 Days Past Due	331	22
Total Loans 30 or More Days Past Due	6,632	8,418
Current Loans	1,605,421	1,391,823
Non-accrual Loans	27,369	48,933
Loans held for investment	1,639,422	1,449,174
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	839	1,062
60 to 89 Days Past Due	383	468
Greater than 90 Days Past Due	0	38
Total Loans 30 or More Days Past Due	1,222	1,568
Current Loans	210,969	188,074
Non-accrual Loans	8,252	16,269
Loans held for investment	220,443	205,911
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	0	933
60 to 89 Days Past Due	475	250
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	475	1,183
Current Loans	95,833	73,933
Non-accrual Loans	272	1,372
Loans held for investment	96,580	76,488
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	100	584
60 to 89 Days Past Due	0	0
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	100	584
Current Loans	98,582	68,427
Non-accrual Loans	2,564	225
Loans held for investment	101,246	69,236
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	939	2,579
60 to 89 Days Past Due	858	718
Greater than 90 Days Past Due	0	38
Total Loans 30 or More Days Past Due	1,797	3,335
Current Loans	405,384	330,434
Non-accrual Loans	11,088	17,866
Loans held for investment	418,269	351,635
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	6,969	3,630
60 to 89 Days Past Due	645	206
Greater than 90 Days Past Due	1,762	1,162
Total Loans 30 or More Days Past Due	9,376	4,998
Current Loans	987,735	856,800
Non-accrual Loans	2,792	6,114
Loans held for investment	999,903	867,912
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	1,624	328
60 to 89 Days Past Due	236	646
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	1,860	974
Current Loans	158,957	163,986
Non-accrual Loans	6,842	8,574
Loans held for investment	167,659	173,534
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	14,224	12,461
60 to 89 Days Past Due	3,348	4,042
Greater than 90 Days Past Due	2,093	1,222
Total Loans 30 or More Days Past Due	19,665	17,725
Current Loans	3,157,497	2,743,043
Non-accrual Loans	48,091	81,487
Loans held for investment	3,225,253	2,842,255
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	3,235	3,303
60 to 89 Days Past Due	482	430
Greater than 90 Days Past Due	6	9
Total Loans 30 or More Days Past Due	3,723	3,742
Current Loans	548,757	471,906
Non-accrual Loans	383	364
Loans held for investment	552,863	476,012
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	988	925
60 to 89 Days Past Due	140	130
Greater than 90 Days Past Due	32	1
Total Loans 30 or More Days Past Due	1,160	1,056
Current Loans	142,432	131,508
Non-accrual Loans	549	475
Loans held for investment	144,141	133,039
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	369	364
60 to 89 Days Past Due	284	187
Greater than 90 Days Past Due	315	515
Total Loans 30 or More Days Past Due	968	1,066
Current Loans	64,484	61,451
Non-accrual Loans	15	19
Loans held for investment	65,467	62,536
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	4,592	4,592
60 to 89 Days Past Due	906	747
Greater than 90 Days Past Due	353	525
Total Loans 30 or More Days Past Due	5,851	5,864
Current Loans	755,673	664,865
Non-accrual Loans	947	858
Loans held for investment	762,471	671,587
Commercial
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	3,659	2,791
60 to 89 Days Past Due	994	1,186
Greater than 90 Days Past Due	147	563
Total Loans 30 or More Days Past Due	4,800	4,540
Current Loans	722,575	660,035
Non-accrual Loans	12,698	11,969
Loans held for investment	740,073	676,544
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	1,125	453
60 to 89 Days Past Due	0	672
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	1,125	1,125
Current Loans	123,288	110,622
Non-accrual Loans	446	125
Loans held for investment	124,859	111,872
Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
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	3,959	1,734
Non-accrual Loans	0	0
Loans held for investment	3,959	1,734
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	23,600	20,297
60 to 89 Days Past Due	5,248	6,647
Greater than 90 Days Past Due	2,593	2,310
Total Loans 30 or More Days Past Due	31,441	29,254
Current Loans	4,762,992	4,180,299
Non-accrual Loans	62,182	94,439
Loans held for investment	4,856,615	4,303,992
Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
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	40,828	40,861
Non-accrual Loans	0	0
Mortgage loans held for sale	40,828	40,861
Total loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	23,600	20,297
60 to 89 Days Past Due	5,248	6,647
Greater than 90 Days Past Due	2,593	2,310
Total Loans 30 or More Days Past Due	31,441	29,254
Current Loans	4,803,820	4,221,160
Non-accrual Loans	62,182	94,439
Total loans	$ 4,897,443	$ 4,344,853