Allowance for Probable Loan Losses (Portfolio Credit Quality By Loan Class) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Loan portfolio by credit quality indicator
Portfolio, total	$ 6,205,846	$ 5,964,688
Pass
Loan portfolio by credit quality indicator
Portfolio, total	5,754,316	5,544,614
Special Review
Loan portfolio by credit quality indicator
Portfolio, total	43,185	101,679
Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	92,935	60,993
Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	272,040	208,997
Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	43,370	48,405
Commercial
Loan portfolio by credit quality indicator
Portfolio, total	914,103	909,667
Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	733,341	720,350
Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	34,695	90,746
Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,066	1,121
Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	123,890	75,038
Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	21,111	22,412
Commercial Real Estate: Other Construction and Land Development
Loan portfolio by credit quality indicator
Portfolio, total	1,838,274	1,716,875
Commercial Real Estate: Other Construction and Land Development | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,773,155	1,648,633
Commercial Real Estate: Other Construction and Land Development | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	918	1,986
Commercial Real Estate: Other Construction and Land Development | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	61,396	61,480
Commercial Real Estate: Other Construction and Land Development | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	2,805	4,776
Commercial Real Estate: Farmland & Commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,960,360	1,943,070
Commercial Real Estate: Farmland & Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,765,602	1,792,542
Commercial Real Estate: Farmland & Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	7,380	7,983
Commercial Real Estate: Farmland & Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	91,869	59,872
Commercial Real Estate: Farmland & Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	86,190	71,863
Commercial Real Estate: Farmland & Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	9,319	10,810
Commercial Real Estate: Multifamily
Loan portfolio by credit quality indicator
Portfolio, total	176,593	140,466
Commercial Real Estate: Multifamily | Pass
Loan portfolio by credit quality indicator
Portfolio, total	176,078	139,914
Commercial Real Estate: Multifamily | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	515	552
Residential First Lien
Loan portfolio by credit quality indicator
Portfolio, total	420,645	421,904
Residential First Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	413,290	413,638
Residential First Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	42	814
Residential First Lien | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	564	616
Residential First Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	6,749	6,836
Residential Junior Lien
Loan portfolio by credit quality indicator
Portfolio, total	658,120	610,318
Residential Junior Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	657,005	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	965	978
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	53,533	55,168
Consumer | Pass
Loan portfolio by credit quality indicator
Portfolio, total	52,381	53,873
Consumer | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,152	1,295
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	184,218	167,220
Foreign | Pass
Loan portfolio by credit quality indicator
Portfolio, total	183,464	166,474
Foreign | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	$ 754	$ 746