Loans and Leases and the Allowance for Credit Losses - Impaired Loans and Leases (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	$ 501,230	$ 498,575
Unpaid principal balance with related allowance	579,049	581,887
Related allowance	82,726	82,643
Recorded investment with no related allowance	278,400	263,880
Unpaid principal balance with no related allowance	377,625	371,907
Recorded investment	779,630	762,455
Unpaid principal balance	956,674	953,794
Related allowance	82,726	82,643
Commercial, Financial, Leasing, etc. [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	144,051	132,340
Unpaid principal balance with related allowance	166,877	165,146
Related allowance	35,195	31,779
Recorded investment with no related allowance	111,023	73,978
Unpaid principal balance with no related allowance	133,100	81,493
Recorded investment	255,074	206,318
Unpaid principal balance	299,977	246,639
Related allowance	35,195	31,779
Commercial Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	105,561	83,955
Unpaid principal balance with related allowance	122,369	96,209
Related allowance	18,932	14,121
Recorded investment with no related allowance	77,147	66,777
Unpaid principal balance with no related allowance	84,677	78,943
Recorded investment	182,708	150,732
Unpaid principal balance	207,046	175,152
Related allowance	18,932	14,121
Residential Builder and Developer [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	6,544	17,632
Unpaid principal balance with related allowance	10,276	22,044
Related allowance	788	805
Recorded investment with no related allowance	42,800	58,820
Unpaid principal balance with no related allowance	68,906	96,722
Recorded investment	49,344	76,452
Unpaid principal balance	79,182	118,766
Related allowance	788	805
Other Commercial Construction [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	2,445	5,480
Unpaid principal balance with related allowance	3,991	6,484
Related allowance	391	900
Recorded investment with no related allowance	10,307	20,738
Unpaid principal balance with no related allowance	28,480	41,035
Recorded investment	12,752	26,218
Unpaid principal balance	32,471	47,519
Related allowance	391	900
Residential [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	83,349	88,970
Unpaid principal balance with related allowance	101,367	107,343
Related allowance	4,775	4,296
Recorded investment with no related allowance	16,232	16,815
Unpaid principal balance with no related allowance	26,626	26,750
Recorded investment	99,581	105,785
Unpaid principal balance	127,993	134,093
Related allowance	4,775	4,296
Residential Alt-A [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	93,168	101,137
Unpaid principal balance with related allowance	107,075	114,565
Related allowance	8,500	11,000
Recorded investment with no related allowance	20,891	26,752
Unpaid principal balance with no related allowance	35,836	46,964
Recorded investment	114,059	127,889
Unpaid principal balance	142,911	161,529
Related allowance	8,500	11,000
Home Equity Lines and Loans [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	23,257	19,771
Unpaid principal balance with related allowance	24,239	20,806
Related allowance	3,541	6,213
Recorded investment	23,257	19,771
Unpaid principal balance	24,239	20,806
Related allowance	3,541	6,213
Automobile [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	23,985	30,317
Unpaid principal balance with related allowance	23,985	30,317
Related allowance	5,118	8,070
Recorded investment	23,985	30,317
Unpaid principal balance	23,985	30,317
Related allowance	5,118	8,070
Other [Member]
Schedule Of Financial Receivables [Line Items]
Recorded investment with related allowance	18,870	18,973
Unpaid principal balance with related allowance	18,870	18,973
Related allowance	5,486	5,459
Recorded investment	18,870	18,973
Unpaid principal balance	18,870	18,973
Related allowance	$ 5,486	$ 5,459