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Allowance for Probable Loan Losses (Portfolio Credit Quality By Loan Class) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Loan portfolio by credit quality indicator
Portfolio, total	$ 6,348,172	$ 5,964,688
Number of additional relationships reclassified from Pass to Watch List - Substandard | item	3
Pass
Loan portfolio by credit quality indicator
Portfolio, total	$ 5,911,001	5,544,614
Special Review
Loan portfolio by credit quality indicator
Portfolio, total	6,612	101,679
Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	45,662	60,993
Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	321,693	208,997
Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	63,204	48,405
Commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,086,467	909,667
Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	905,707	720,350
Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total		90,746
Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	3,170	1,121
Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	159,643	75,038
Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	17,947	22,412
Commercial Real Estate: Other Construction and Land Development
Loan portfolio by credit quality indicator
Portfolio, total	1,683,550	1,716,875
Commercial Real Estate: Other Construction and Land Development | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,616,604	1,648,633
Commercial Real Estate: Other Construction and Land Development | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	1,288	1,986
Commercial Real Estate: Other Construction and Land Development | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	672
Commercial Real Estate: Other Construction and Land Development | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	62,531	61,480
Commercial Real Estate: Other Construction and Land Development | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	2,455	4,776
Commercial Real Estate: Farmland & Commercial
Loan portfolio by credit quality indicator
Portfolio, total	2,043,285	1,943,070
Commercial Real Estate: Farmland & Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,863,763	1,792,542
Commercial Real Estate: Farmland & Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	5,134	7,983
Commercial Real Estate: Farmland & Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	41,820	59,872
Commercial Real Estate: Farmland & Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	99,445	71,863
Commercial Real Estate: Farmland & Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	33,123	10,810
Commercial Real Estate: Multifamily
Loan portfolio by credit quality indicator
Portfolio, total	192,916	140,466
Commercial Real Estate: Multifamily | Pass
Loan portfolio by credit quality indicator
Portfolio, total	192,440	139,914
Commercial Real Estate: Multifamily | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	476	552
Residential First Lien
Loan portfolio by credit quality indicator
Portfolio, total	432,777	421,904
Residential First Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	425,811	413,638
Residential First Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	40	814
Residential First Lien | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	74	616
Residential First Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	6,852	6,836
Residential Junior Lien
Loan portfolio by credit quality indicator
Portfolio, total	700,748	610,318
Residential Junior Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	699,875	609,190
Residential Junior Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	150	150
Residential Junior Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	723	978
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	49,543	55,168
Consumer | Pass
Loan portfolio by credit quality indicator
Portfolio, total	48,262	53,873
Consumer | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,281	1,295
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	158,886	167,220
Foreign | Pass
Loan portfolio by credit quality indicator
Portfolio, total	158,539	166,474
Foreign | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	$ 347	$ 746

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The number of relationships that were reclassified from pass category to watch list - substandard category.

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- Definition

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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