Loans and Leases (Age Analysis of Past Due Financing Receivables) (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Financing Receivables That Are Accruing [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	$ 21,723,000	$ 57,234,000
60-89 Days Past Due	8,495,000	11,389,000
90 Days and Greater	10,303,000	9,757,000
Total Past Due	40,521,000	78,380,000
Current	13,275,694,000	13,396,891,000
Total Financing Receivables, Accruing	13,316,215,000	13,475,271,000
Financing Receivables That Are Accruing [Member] | Originated Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	19,146,000	46,031,000
60-89 Days Past Due	7,398,000	9,381,000
90 Days and Greater	5,565,000	7,302,000
Total Past Due	32,109,000	62,714,000
Current	11,868,687,000	11,787,333,000
Total Financing Receivables, Accruing	11,900,796,000	11,850,047,000
Financing Receivables That Are Accruing [Member] | Purchased Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	2,577,000	11,203,000
60-89 Days Past Due	1,097,000	2,008,000
90 Days and Greater	4,738,000	2,455,000
Total Past Due	8,412,000	15,666,000
Current	1,407,007,000	1,609,558,000
Total Financing Receivables, Accruing	1,415,419,000	1,625,224,000
Financing Receivables That Are Accruing [Member] | Commercial, Financial, And Agricultural [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	2,157,000	3,640,000
60-89 Days Past Due	974,000	518,000
90 Days and Greater	65,000	127,000
Total Past Due	3,196,000	4,285,000
Current	2,335,884,000	2,373,735,000
Total Financing Receivables, Accruing	2,339,080,000	2,378,020,000
Financing Receivables That Are Accruing [Member] | Real Estate - Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	2,600,000	1,631,000
60-89 Days Past Due	87,000	903,000
90 Days and Greater	0	418,000
Total Past Due	2,687,000	2,952,000
Current	807,580,000	719,695,000
Total Financing Receivables, Accruing	810,267,000	722,647,000
Financing Receivables That Are Accruing [Member] | Real Estate Secured - Residential [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	7,866,000	27,441,000
60-89 Days Past Due	4,692,000	6,223,000
90 Days and Greater	9,170,000	7,274,000
Total Past Due	21,728,000	40,938,000
Current	4,127,562,000	4,140,127,000
Total Financing Receivables, Accruing	4,149,290,000	4,181,065,000
Financing Receivables That Are Accruing [Member] | Real Estate Secured - Commercial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	3,728,000	11,583,000
60-89 Days Past Due	1,218,000	1,840,000
90 Days and Greater	822,000	667,000
Total Past Due	5,768,000	14,090,000
Current	3,956,383,000	4,008,579,000
Total Financing Receivables, Accruing	3,962,151,000	4,022,669,000
Financing Receivables That Are Accruing [Member] | Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	4,555,000	8,664,000
60-89 Days Past Due	1,407,000	1,537,000
90 Days and Greater	199,000	983,000
Total Past Due	6,161,000	11,184,000
Current	724,486,000	941,769,000
Total Financing Receivables, Accruing	730,647,000	952,953,000
Financing Receivables That Are Accruing [Member] | Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	817,000	4,275,000
60-89 Days Past Due	117,000	368,000
90 Days and Greater	47,000	288,000
Total Past Due	981,000	4,931,000
Current	1,323,799,000	1,212,986,000
Total Financing Receivables, Accruing	1,324,780,000	1,217,917,000
Financing Receivables That Are Nonaccruing [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	5,953,000	8,937,000
60-89 Days Past Due	2,261,000	5,890,000
90 Days and Greater	63,558,000	46,788,000
Total Past Due	71,772,000	61,615,000
Current	37,734,000	39,200,000
Total Financing Receivables, Nonaccruing	109,506,000	100,815,000
Financing Receivables That Are Nonaccruing [Member] | Originated Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	5,658,000	8,205,000
60-89 Days Past Due	2,131,000	3,806,000
90 Days and Greater	51,740,000	39,553,000
Total Past Due	59,529,000	51,564,000
Current	32,844,000	29,335,000
Total Financing Receivables, Nonaccruing	92,373,000	80,899,000
Financing Receivables That Are Nonaccruing [Member] | Purchased Loans And Leases [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	295,000	732,000
60-89 Days Past Due	130,000	2,084,000
90 Days and Greater	11,818,000	7,235,000
Total Past Due	12,243,000	10,051,000
Current	4,890,000	9,865,000
Total Financing Receivables, Nonaccruing	17,133,000	19,916,000
Financing Receivables That Are Nonaccruing [Member] | Commercial, Financial, And Agricultural [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	4,235,000	4,832,000
60-89 Days Past Due	708,000	855,000
90 Days and Greater	10,090,000	4,850,000
Total Past Due	15,033,000	10,537,000
Current	8,088,000	6,290,000
Total Financing Receivables, Nonaccruing	23,121,000	16,827,000
Financing Receivables That Are Nonaccruing [Member] | Real Estate - Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	0	2,176,000
60-89 Days Past Due	87,000	788,000
90 Days and Greater	3,675,000	5,320,000
Total Past Due	3,762,000	8,284,000
Current	3,463,000	4,946,000
Total Financing Receivables, Nonaccruing	7,225,000	13,230,000
Financing Receivables That Are Nonaccruing [Member] | Real Estate Secured - Residential [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	512,000	609,000
60-89 Days Past Due	472,000	497,000
90 Days and Greater	15,734,000	16,518,000
Total Past Due	16,718,000	17,624,000
Current	6,935,000	5,741,000
Total Financing Receivables, Nonaccruing	23,653,000	23,365,000
Financing Receivables That Are Nonaccruing [Member] | Real Estate Secured - Commercial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
30-59 Days Past Due	1,206,000	1,320,000
60-89 Days Past Due	909,000	3,551,000
90 Days and Greater	34,029,000	19,952,000
Total Past Due	36,144,000	24,823,000
Current	18,340,000	21,324,000
Total Financing Receivables, Nonaccruing	54,484,000	46,147,000
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	0	0
90 Days and Greater	0	0
Total Past Due	0	0
Current	40,000	47,000
Total Financing Receivables, Nonaccruing	40,000	47,000
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	85,000	199,000
90 Days and Greater	30,000	148,000
Total Past Due	115,000	347,000
Current	868,000	852,000
Total Financing Receivables, Nonaccruing	$ 983,000	$ 1,199,000