Allowance for Probable Loan Losses (Aging By Loan Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing receivable recorded investment
Past due	$ 65,097	$ 68,273
Past due 90 days or greater and still accruing	8,558	11,616
Loans, current	5,870,477	5,882,641
Total loans	5,935,574	5,950,914
30 to 59 Days
Financing receivable recorded investment
Past due	29,856	15,584
60 to 89 Days
Financing receivable recorded investment
Past due	5,746	5,219
90 Days or Greater
Financing receivable recorded investment
Past due	29,495	47,470
Commercial
Financing receivable recorded investment
Past due	28,534	32,916
Past due 90 days or greater and still accruing	392	2,566
Loans, current	917,641	933,936
Total loans	946,175	966,852
Commercial | 30 to 59 Days
Financing receivable recorded investment
Past due	16,109	3,361
Commercial | 60 to 89 Days
Financing receivable recorded investment
Past due	2,069	940
Commercial | 90 Days or Greater
Financing receivable recorded investment
Past due	10,356	28,615
Commercial Real Estate: Other Construction and Land Development
Financing receivable recorded investment
Past due	7,035	3,988
Past due 90 days or greater and still accruing	125
Loans, current	1,701,117	1,645,839
Total loans	1,708,152	1,649,827
Commercial Real Estate: Other Construction and Land Development | 30 to 59 Days
Financing receivable recorded investment
Past due	3,590	193
Commercial Real Estate: Other Construction and Land Development | 60 to 89 Days
Financing receivable recorded investment
Past due	273	293
Commercial Real Estate: Other Construction and Land Development | 90 Days or Greater
Financing receivable recorded investment
Past due	3,172	3,502
Commercial Real Estate: Farmland & Commercial
Financing receivable recorded investment
Past due	14,165	12,304
Past due 90 days or greater and still accruing	1,642	3,373
Loans, current	1,916,693	1,983,144
Total loans	1,930,858	1,995,448
Commercial Real Estate: Farmland & Commercial | 30 to 59 Days
Financing receivable recorded investment
Past due	4,399	2,684
Commercial Real Estate: Farmland & Commercial | 60 to 89 Days
Financing receivable recorded investment
Past due	1,021	1,328
Commercial Real Estate: Farmland & Commercial | 90 Days or Greater
Financing receivable recorded investment
Past due	8,745	8,292
Commercial Real Estate: Multifamily
Financing receivable recorded investment
Past due	653	1,317
Past due 90 days or greater and still accruing	442	49
Loans, current	147,918	138,131
Total loans	148,571	139,448
Commercial Real Estate: Multifamily | 30 to 59 Days
Financing receivable recorded investment
Past due	47	49
Commercial Real Estate: Multifamily | 60 to 89 Days
Financing receivable recorded investment
Past due		442
Commercial Real Estate: Multifamily | 90 Days or Greater
Financing receivable recorded investment
Past due	606	826
Residential First Lien
Financing receivable recorded investment
Past due	9,937	11,139
Past due 90 days or greater and still accruing	4,513	4,093
Loans, current	402,403	399,105
Total loans	412,340	410,244
Residential First Lien | 30 to 59 Days
Financing receivable recorded investment
Past due	3,599	5,299
Residential First Lien | 60 to 89 Days
Financing receivable recorded investment
Past due	1,598	1,545
Residential First Lien | 90 Days or Greater
Financing receivable recorded investment
Past due	4,740	4,295
Residential Junior Lien
Financing receivable recorded investment
Past due	1,606	1,772
Past due 90 days or greater and still accruing	613	640
Loans, current	555,266	550,566
Total loans	556,872	552,338
Residential Junior Lien | 30 to 59 Days
Financing receivable recorded investment
Past due	499	713
Residential Junior Lien | 60 to 89 Days
Financing receivable recorded investment
Past due	462	413
Residential Junior Lien | 90 Days or Greater
Financing receivable recorded investment
Past due	645	646
Consumer
Financing receivable recorded investment
Past due	1,404	1,308
Past due 90 days or greater and still accruing	409	453
Loans, current	54,521	56,436
Total loans	55,925	57,744
Consumer | 30 to 59 Days
Financing receivable recorded investment
Past due	704	646
Consumer | 60 to 89 Days
Financing receivable recorded investment
Past due	256	175
Consumer | 90 Days or Greater
Financing receivable recorded investment
Past due	444	487
Foreign
Financing receivable recorded investment
Past due	1,763	3,529
Past due 90 days or greater and still accruing	422	442
Loans, current	174,918	175,484
Total loans	176,681	179,013
Foreign | 30 to 59 Days
Financing receivable recorded investment
Past due	909	2,639
Foreign | 60 to 89 Days
Financing receivable recorded investment
Past due	67	83
Foreign | 90 Days or Greater
Financing receivable recorded investment
Past due	$ 787	$ 807