Loans and Leases - Age Analysis of Past Due Loans, by Class (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,626,787	$ 11,247,038
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,852,607	3,815,708
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	2,453,868	2,318,015
Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	190,881	177,824
Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	6,497,356	6,311,547
Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,676,349	1,644,621
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,350,502	1,263,053
Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	942,801	875,551
Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,118,970	1,110,976
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	40,809	41,290
Originated Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	36,581	41,275
> 90 Days Past Due and Still Accruing	5,917	9,248
Non-Accrual	45,332	45,113
Total Past Due	87,830	95,636
Current	10,156,747	9,570,509
Total Loans	10,244,577	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	6,054	9,601
> 90 Days Past Due and Still Accruing	3	313
Non-Accrual	24,652	24,132
Total Past Due	30,709	34,046
Current	3,147,510	2,997,764
Total Loans	3,178,219	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	2,800	2,446
> 90 Days Past Due and Still Accruing	3	3
Non-Accrual	8,966	8,310
Total Past Due	11,769	10,759
Current	2,331,444	2,187,034
Total Loans	2,343,213	2,197,793
Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	818	961
> 90 Days Past Due and Still Accruing		43
Non-Accrual	699	722
Total Past Due	1,517	1,726
Current	189,364	176,098
Total Loans	190,881	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	9,672	13,008
> 90 Days Past Due and Still Accruing	6	359
Non-Accrual	34,317	33,164
Total Past Due	43,995	46,531
Current	5,668,318	5,360,896
Total Loans	5,712,313	5,407,427
Originated Loans and Leases [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	9,414	9,333
> 90 Days Past Due and Still Accruing	2,969	3,617
Non-Accrual	5,656	7,117
Total Past Due	18,039	20,067
Current	1,605,251	1,559,703
Total Loans	1,623,290	1,579,770
Originated Loans and Leases [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	8,198	8,709
> 90 Days Past Due and Still Accruing	1,536	3,891
Non-Accrual	3,767	2,964
Total Past Due	13,501	15,564
Current	940,339	802,022
Total Loans	953,840	817,586
Originated Loans and Leases [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	7,040	7,804
> 90 Days Past Due and Still Accruing	358	684
Non-Accrual	898	1,149
Total Past Due	8,296	9,637
Current	933,555	864,008
Total Loans	941,851	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	2,192	2,408
> 90 Days Past Due and Still Accruing	975	562
Non-Accrual	694	719
Total Past Due	3,861	3,689
Current	968,613	942,738
Total Loans	972,474	946,427
Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	65	13
> 90 Days Past Due and Still Accruing	73	135
Total Past Due	138	148
Current	40,671	41,142
Total Loans	40,809	41,290
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	20,838	24,678
> 90 Days Past Due and Still Accruing	30,090	38,024
Non-Accrual	64
Total Past Due	50,992	62,702
Current	1,419,034	1,612,959
Discount	(87,816)	(94,768)
Total Loans	1,382,210	1,580,893
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	10,618	12,076
> 90 Days Past Due and Still Accruing	11,098	12,368
Total Past Due	21,716	24,444
Current	691,401	799,991
Discount	(38,729)	(40,537)
Total Loans	674,388	783,898
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	528	687
> 90 Days Past Due and Still Accruing	756	1,968
Non-Accrual	64
Total Past Due	1,348	2,655
Current	117,132	127,535
Discount	(7,825)	(9,968)
Total Loans	110,655	120,222
Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	11,146	12,763
> 90 Days Past Due and Still Accruing	11,854	14,336
Non-Accrual	64
Total Past Due	23,064	27,099
Current	808,533	927,526
Discount	(46,554)	(50,505)
Total Loans	785,043	904,120
Acquired Loans [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,108	2,670
> 90 Days Past Due and Still Accruing	1,057	1,443
Total Past Due	2,165	4,113
Current	49,963	59,532
Discount	931	1,206
Total Loans	53,059	64,851
Acquired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	7,909	8,159
> 90 Days Past Due and Still Accruing	15,688	19,936
Total Past Due	23,597	28,095
Current	410,919	456,810
Discount	(37,854)	(39,438)
Total Loans	396,662	445,467
Acquired Loans [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	21	38
> 90 Days Past Due and Still Accruing	17	30
Total Past Due	38	68
Current	1,149	2,179
Discount	(237)	(341)
Total Loans	950	1,906
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	654	1,048
> 90 Days Past Due and Still Accruing	1,474	2,279
Total Past Due	2,128	3,327
Current	148,470	166,912
Discount	(4,102)	(5,690)
Total Loans	$ 146,496	$ 164,549