Loans and Leases (Age Analysis of Past Due Financing Receivables) (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Financing Receivables That Are Accruing [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	$ 23,731,000	$ 57,241,000
60-89 Days Past Due	16,065,000	22,754,000
90 Days and Greater	8,655,000	8,209,000
Total Past Due	48,451,000	88,204,000
Current	13,226,027,000	12,708,770,000
Total Financing Receivables,Accruing	13,274,478,000	12,796,974,000
Financing Receivables That Are Accruing [Member] | Originated Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	20,599,000	51,679,000
60-89 Days Past Due	13,007,000	21,471,000
90 Days and Greater	7,347,000	5,720,000
Total Past Due	40,953,000	78,870,000
Current	11,495,358,000	10,596,166,000
Total Financing Receivables,Accruing	11,536,311,000	10,675,036,000
Financing Receivables That Are Accruing [Member] | Purchased Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	3,132,000	5,562,000
60-89 Days Past Due	3,058,000	1,283,000
90 Days and Greater	1,308,000	2,489,000
Total Past Due	7,498,000	9,334,000
Current	1,730,669,000	2,112,604,000
Total Financing Receivables,Accruing	1,738,167,000	2,121,938,000
Financing Receivables That Are Accruing [Member] | Commercial, Financial, And Agricultural [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	2,759,000	5,163,000
60-89 Days Past Due	1,428,000	762,000
90 Days and Greater	224,000	359,000
Total Past Due	4,411,000	6,284,000
Current	2,259,276,000	2,256,863,000
Total Financing Receivables,Accruing	2,263,687,000	2,263,147,000
Financing Receivables That Are Accruing [Member] | Real Estate - Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	1,150,000	8,568,000
60-89 Days Past Due	1,438,000	1,614,000
90 Days and Greater	722,000	157,000
Total Past Due	3,310,000	10,339,000
Current	745,439,000	822,625,000
Total Financing Receivables,Accruing	748,749,000	832,964,000
Financing Receivables That Are Accruing [Member] | Real Estate Secured - Residential [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	9,095,000	19,544,000
60-89 Days Past Due	6,171,000	4,467,000
90 Days and Greater	5,272,000	5,547,000
Total Past Due	20,538,000	29,558,000
Current	4,097,106,000	4,007,820,000
Total Financing Receivables,Accruing	4,117,644,000	4,037,378,000
Financing Receivables That Are Accruing [Member] | Real Estate Secured - Commercial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	3,879,000	9,623,000
60-89 Days Past Due	5,444,000	13,746,000
90 Days and Greater	1,824,000	1,394,000
Total Past Due	11,147,000	24,763,000
Current	4,052,276,000	3,897,224,000
Total Financing Receivables,Accruing	4,063,423,000	3,921,987,000
Financing Receivables That Are Accruing [Member] | Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	5,814,000	8,898,000
60-89 Days Past Due	1,387,000	1,678,000
90 Days and Greater	448,000	545,000
Total Past Due	7,649,000	11,121,000
Current	927,291,000	831,388,000
Total Financing Receivables,Accruing	934,940,000	842,509,000
Financing Receivables That Are Accruing [Member] | Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	1,034,000	5,445,000
60-89 Days Past Due	197,000	487,000
90 Days and Greater	165,000	207,000
Total Past Due	1,396,000	6,139,000
Current	1,144,639,000	892,850,000
Total Financing Receivables,Accruing	1,146,035,000	898,989,000
Financing Receivables That Are Nonaccruing [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	4,300,000	4,067,000
60-89 Days Past Due	4,752,000	2,784,000
90 Days and Greater	61,050,000	70,507,000
Total Past Due	70,102,000	77,358,000
Current	31,874,000	20,409,000
Total Financing Receivables, Nonaccruing	101,976,000	97,767,000
Financing Receivables That Are Nonaccruing [Member] | Originated Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	2,501,000	4,067,000
60-89 Days Past Due	3,802,000	2,379,000
90 Days and Greater	54,801,000	65,830,000
Total Past Due	61,104,000	72,276,000
Current	25,048,000	18,146,000
Total Financing Receivables, Nonaccruing	86,152,000	90,422,000
Financing Receivables That Are Nonaccruing [Member] | Purchased Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	1,799,000	0
60-89 Days Past Due	950,000	405,000
90 Days and Greater	6,249,000	4,677,000
Total Past Due	8,998,000	5,082,000
Current	6,826,000	2,263,000
Total Financing Receivables, Nonaccruing	15,824,000	7,345,000
Financing Receivables That Are Nonaccruing [Member] | Commercial, Financial, And Agricultural [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	7,000	631,000
60-89 Days Past Due	354,000	649,000
90 Days and Greater	5,644,000	6,068,000
Total Past Due	6,005,000	7,348,000
Current	4,043,000	3,116,000
Total Financing Receivables, Nonaccruing	10,048,000	10,464,000
Financing Receivables That Are Nonaccruing [Member] | Real Estate - Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	794,000	0
60-89 Days Past Due	390,000	405,000
90 Days and Greater	14,498,000	14,047,000
Total Past Due	15,682,000	14,452,000
Current	815,000	365,000
Total Financing Receivables, Nonaccruing	16,497,000	14,817,000
Financing Receivables That Are Nonaccruing [Member] | Real Estate Secured - Residential [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	188,000	953,000
60-89 Days Past Due	977,000	452,000
90 Days and Greater	16,805,000	19,551,000
Total Past Due	17,970,000	20,956,000
Current	9,908,000	7,484,000
Total Financing Receivables, Nonaccruing	27,878,000	28,440,000
Financing Receivables That Are Nonaccruing [Member] | Real Estate Secured - Commercial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	3,311,000	2,483,000
60-89 Days Past Due	2,827,000	622,000
90 Days and Greater	23,874,000	30,433,000
Total Past Due	30,012,000	33,538,000
Current	15,894,000	9,083,000
Total Financing Receivables, Nonaccruing	45,906,000	42,621,000
Financing Receivables That Are Nonaccruing [Member] | Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	89,000	0
90 Days and Greater	50,000	0
Total Past Due	139,000	0
Current	38,000	43,000
Total Financing Receivables, Nonaccruing	177,000	43,000
Financing Receivables That Are Nonaccruing [Member] | Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	115,000	656,000
90 Days and Greater	179,000	408,000
Total Past Due	294,000	1,064,000
Current	1,176,000	318,000
Total Financing Receivables, Nonaccruing	$ 1,470,000	$ 1,382,000