Allowance for Probable Loan Losses (Portfolio Credit Quality By Loan Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Loan portfolio by credit quality indicator
Portfolio, total	$ 5,935,574	$ 5,950,914
Pass
Loan portfolio by credit quality indicator
Portfolio, total	5,534,164	5,529,707
Special Review
Loan portfolio by credit quality indicator
Portfolio, total	1,036	45,599
Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	148,738	83,069
Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	207,664	232,091
Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	43,972	60,448
Commercial
Loan portfolio by credit quality indicator
Portfolio, total	946,175	966,852
Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	770,631	771,999
Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total		42,152
Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	90,096	31,539
Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	70,590	90,215
Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	14,858	30,946
Commercial Real Estate: Other Construction and Land Development
Loan portfolio by credit quality indicator
Portfolio, total	1,708,152	1,649,827
Commercial Real Estate: Other Construction and Land Development | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,641,268	1,582,683
Commercial Real Estate: Other Construction and Land Development | Special Review
Loan portfolio by credit quality indicator
Portfolio, total		1,164
Commercial Real Estate: Other Construction and Land Development | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	14,665	13,765
Commercial Real Estate: Other Construction and Land Development | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	46,254	45,994
Commercial Real Estate: Other Construction and Land Development | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	5,965	6,221
Commercial Real Estate: Farmland & Commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,930,858	1,995,448
Commercial Real Estate: Farmland & Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,786,473	1,849,587
Commercial Real Estate: Farmland & Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	1,036	2,283
Commercial Real Estate: Farmland & Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	39,516	37,765
Commercial Real Estate: Farmland & Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	90,193	92,008
Commercial Real Estate: Farmland & Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	13,640	13,806
Commercial Real Estate: Multifamily
Loan portfolio by credit quality indicator
Portfolio, total	148,571	139,448
Commercial Real Estate: Multifamily | Pass
Loan portfolio by credit quality indicator
Portfolio, total	147,841	138,546
Commercial Real Estate: Multifamily | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	566	125
Commercial Real Estate: Multifamily | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	164	777
Residential First Lien
Loan portfolio by credit quality indicator
Portfolio, total	412,340	410,244
Residential First Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	401,705	401,053
Residential First Lien | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	4,216
Residential First Lien | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	61	3,492
Residential First Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	6,358	5,699
Residential Junior Lien
Loan portfolio by credit quality indicator
Portfolio, total	556,872	552,338
Residential Junior Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	555,595	551,138
Residential Junior Lien | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	245
Residential Junior Lien | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total		250
Residential Junior Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,032	950
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	55,925	57,744
Consumer | Pass
Loan portfolio by credit quality indicator
Portfolio, total	54,715	56,440
Consumer | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total		7
Consumer | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,210	1,297
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	176,681	179,013
Foreign | Pass
Loan portfolio by credit quality indicator
Portfolio, total	175,936	178,261
Foreign | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total	$ 745	$ 752