Loans and Leases - Age Analysis of Past Due Loans, by Class (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,873,645	$ 11,247,038
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,949,246	3,815,708
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	2,491,355	2,318,015
Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	199,130	177,824
Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	6,639,731	6,311,547
Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,692,638	1,644,621
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,386,386	1,263,053
Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	974,028	875,551
Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,127,002	1,110,976
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	53,860	41,290
Originated Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	43,330	41,275
> 90 Days Past Due and Still Accruing	6,000	9,248
Non-Accrual	45,436	45,113
Total Past Due	94,766	95,636
Current	10,524,172	9,570,509
Total Loans	10,618,938	9,666,145
Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	6,040	9,601
> 90 Days Past Due and Still Accruing	3	313
Non-Accrual	25,262	24,132
Total Past Due	31,305	34,046
Current	3,291,364	2,997,764
Total Loans	3,322,669	3,031,810
Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	3,854	2,446
> 90 Days Past Due and Still Accruing	3	3
Non-Accrual	9,529	8,310
Total Past Due	13,386	10,759
Current	2,396,800	2,187,034
Total Loans	2,410,186	2,197,793
Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	709	961
> 90 Days Past Due and Still Accruing	14	43
Non-Accrual	835	722
Total Past Due	1,558	1,726
Current	197,572	176,098
Total Loans	199,130	177,824
Originated Loans and Leases [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	10,603	13,008
> 90 Days Past Due and Still Accruing	20	359
Non-Accrual	35,626	33,164
Total Past Due	46,249	46,531
Current	5,885,736	5,360,896
Total Loans	5,931,985	5,407,427
Originated Loans and Leases [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	9,874	9,333
> 90 Days Past Due and Still Accruing	3,326	3,617
Non-Accrual	4,718	7,117
Total Past Due	17,918	20,067
Current	1,625,427	1,559,703
Total Loans	1,643,345	1,579,770
Originated Loans and Leases [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	11,121	8,709
> 90 Days Past Due and Still Accruing	1,334	3,891
Non-Accrual	2,971	2,964
Total Past Due	15,426	15,564
Current	997,828	802,022
Total Loans	1,013,254	817,586
Originated Loans and Leases [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	8,213	7,804
> 90 Days Past Due and Still Accruing	522	684
Non-Accrual	1,133	1,149
Total Past Due	9,868	9,637
Current	963,348	864,008
Total Loans	973,216	873,645
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	3,385	2,408
> 90 Days Past Due and Still Accruing	629	562
Non-Accrual	988	719
Total Past Due	5,002	3,689
Current	998,276	942,738
Total Loans	1,003,278	946,427
Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	134	13
> 90 Days Past Due and Still Accruing	169	135
Total Past Due	303	148
Current	53,557	41,142
Total Loans	53,860	41,290
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	21,604	24,678
> 90 Days Past Due and Still Accruing	28,551	38,024
Non-Accrual	1,862
Total Past Due	52,017	62,702
Current	1,288,288	1,612,959
Discount	(85,598)	(94,768)
Total Loans	1,254,707	1,580,893
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	10,510	12,076
> 90 Days Past Due and Still Accruing	11,108	12,368
Non-Accrual	1,303
Total Past Due	22,921	24,444
Current	641,768	799,991
Discount	(38,112)	(40,537)
Total Loans	626,577	783,898
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	686	687
> 90 Days Past Due and Still Accruing	527	1,968
Non-Accrual	107
Total Past Due	1,320	2,655
Current	87,163	127,535
Discount	(7,314)	(9,968)
Total Loans	81,169	120,222
Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	11,196	12,763
> 90 Days Past Due and Still Accruing	11,635	14,336
Non-Accrual	1,410
Total Past Due	24,241	27,099
Current	728,931	927,526
Discount	(45,426)	(50,505)
Total Loans	707,746	904,120
Acquired Loans [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	670	2,670
> 90 Days Past Due and Still Accruing	834	1,443
Total Past Due	1,504	4,113
Current	46,981	59,532
Discount	808	1,206
Total Loans	49,293	64,851
Acquired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	8,607	8,159
> 90 Days Past Due and Still Accruing	15,261	19,936
Total Past Due	23,868	28,095
Current	386,425	456,810
Discount	(37,161)	(39,438)
Total Loans	373,132	445,467
Acquired Loans [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	26	38
> 90 Days Past Due and Still Accruing	11	30
Total Past Due	37	68
Current	801	2,179
Discount	(26)	(341)
Total Loans	812	1,906
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,105	1,048
> 90 Days Past Due and Still Accruing	810	2,279
Non-Accrual	452
Total Past Due	2,367	3,327
Current	125,150	166,912
Discount	(3,793)	(5,690)
Total Loans	$ 123,724	$ 164,549