Allowance for Probable Loan Losses (Aging By Loan Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing receivable recorded investment
Past due	$ 82,493	$ 77,053
Past due 90 days or Greater and Still Accruing	8,187	7,257
Loans, current	6,370,610	6,271,119
Total loans	6,453,103	6,348,172
30 to 59 Days
Financing receivable recorded investment
Past due	15,288	15,855
60 to 89 Days
Financing receivable recorded investment
Past due	10,132	4,429
90 Days or Greater
Financing receivable recorded investment
Past due	57,073	56,769
Commercial
Financing receivable recorded investment
Past due	21,957	22,496
Past due 90 days or Greater and Still Accruing	962	537
Loans, current	1,101,139	1,063,971
Total loans	1,123,096	1,086,467
Commercial \| 30 to 59 Days
Financing receivable recorded investment
Past due	2,492	3,790
Commercial \| 60 to 89 Days
Financing receivable recorded investment
Past due	894	398
Commercial \| 90 Days or Greater
Financing receivable recorded investment
Past due	18,571	18,308
Commercial Real Estate:Other Construction and Land Development
Financing receivable recorded investment
Past due	7,023	1,482
Past due 90 days or Greater and Still Accruing	211	6
Loans, current	1,718,606	1,682,068
Total loans	1,725,629	1,683,550
Commercial Real Estate:Other Construction and Land Development \| 30 to 59 Days
Financing receivable recorded investment
Past due	964	354
Commercial Real Estate:Other Construction and Land Development \| 60 to 89 Days
Financing receivable recorded investment
Past due	5,034	308
Commercial Real Estate:Other Construction and Land Development \| 90 Days or Greater
Financing receivable recorded investment
Past due	1,025	820
Commercial Real Estate: Farmland and Commercial
Financing receivable recorded investment
Past due	37,350	35,576
Past due 90 days or Greater and Still Accruing	646	954
Loans, current	2,054,489	2,007,709
Total loans	2,091,839	2,043,285
Commercial Real Estate: Farmland and Commercial \| 30 to 59 Days
Financing receivable recorded investment
Past due	4,415	3,925
Commercial Real Estate: Farmland and Commercial \| 60 to 89 Days
Financing receivable recorded investment
Past due	2,525	518
Commercial Real Estate: Farmland and Commercial \| 90 Days or Greater
Financing receivable recorded investment
Past due	30,410	31,133
Commercial Real Estate: Multifamily
Financing receivable recorded investment
Past due	682	560
Past due 90 days or Greater and Still Accruing	37
Loans, current	178,634	192,356
Total loans	179,316	192,916
Commercial Real Estate: Multifamily \| 30 to 59 Days
Financing receivable recorded investment
Past due	175	84
Commercial Real Estate: Multifamily \| 90 Days or Greater
Financing receivable recorded investment
Past due	507	476
Residential First Lien
Financing receivable recorded investment
Past due	8,683	10,848
Past due 90 days or Greater and Still Accruing	4,917	3,861
Loans, current	418,996	421,929
Total loans	427,679	432,777
Residential First Lien \| 30 to 59 Days
Financing receivable recorded investment
Past due	2,466	4,295
Residential First Lien \| 60 to 89 Days
Financing receivable recorded investment
Past due	1,097	2,458
Residential First Lien \| 90 Days or Greater
Financing receivable recorded investment
Past due	5,120	4,095
Residential Junior Lien
Financing receivable recorded investment
Past due	2,183	3,000
Past due 90 days or Greater and Still Accruing	793	1,099
Loans, current	699,072	697,748
Total loans	701,255	700,748
Residential Junior Lien \| 30 to 59 Days
Financing receivable recorded investment
Past due	1,184	1,310
Residential Junior Lien \| 60 to 89 Days
Financing receivable recorded investment
Past due	202	580
Residential Junior Lien \| 90 Days or Greater
Financing receivable recorded investment
Past due	797	1,110
Consumer
Financing receivable recorded investment
Past due	901	1,126
Past due 90 days or Greater and Still Accruing	47	133
Loans, current	45,877	48,417
Total loans	46,778	49,543
Consumer \| 30 to 59 Days
Financing receivable recorded investment
Past due	767	868
Consumer \| 60 to 89 Days
Financing receivable recorded investment
Past due	65	98
Consumer \| 90 Days or Greater
Financing receivable recorded investment
Past due	69	160
Foreign
Financing receivable recorded investment
Past due	3,714	1,965
Past due 90 days or Greater and Still Accruing	574	667
Loans, current	153,797	156,921
Total loans	157,511	158,886
Foreign \| 30 to 59 Days
Financing receivable recorded investment
Past due	2,825	1,229
Foreign \| 60 to 89 Days
Financing receivable recorded investment
Past due	315	69
Foreign \| 90 Days or Greater
Financing receivable recorded investment
Past due	$ 574	$ 667

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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Financing receivables that are current.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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