Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, by Class (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 10,967,860	$ 9,506,094
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,790,164	3,245,209
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	2,247,605	1,881,474
Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	171,615	158,895
Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	6,209,384	5,285,578
Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,579,312	1,467,236
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,231,796	1,086,739
Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	805,836	655,587
Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,087,271	965,771
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	54,261	45,183
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	35,899	37,342
> 90 Days Past Due and Still Accruing	7,085	7,971
Non- Accrual	55,095	58,755
Total Past Due	98,079	104,068
Current	9,152,549	8,050,697
Total Loans	9,250,628	8,154,765
Originated Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	3,711	5,428
> 90 Days Past Due and Still Accruing	132	252
Non- Accrual	33,710	40,960
Total Past Due	37,553	46,640
Current	2,892,593	2,593,788
Total Loans	2,930,146	2,640,428
Originated Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,478	2,066
> 90 Days Past Due and Still Accruing	6	8
Non- Accrual	8,439	6,643
Total Past Due	10,923	8,717
Current	2,093,636	1,752,951
Total Loans	2,104,559	1,761,668
Originated Loans [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	985	714
> 90 Days Past Due and Still Accruing
Non- Accrual	651	734
Total Past Due	1,636	1,448
Current	169,979	157,447
Total Loans	171,615	158,895
Originated Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	7,174	8,208
> 90 Days Past Due and Still Accruing	138	260
Non- Accrual	42,800	48,337
Total Past Due	50,112	56,805
Current	5,156,208	4,504,186
Total Loans	5,206,320	4,560,991
Originated Loans [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	11,102	9,038
> 90 Days Past Due and Still Accruing	3,498	3,753
Non- Accrual	6,761	4,686
Total Past Due	21,361	17,477
Current	1,487,735	1,370,518
Total Loans	1,509,096	1,387,995
Originated Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	9,646	12,681
> 90 Days Past Due and Still Accruing	2,242	2,401
Non- Accrual	3,471	4,260
Total Past Due	15,359	19,342
Current	747,384	658,885
Total Loans	762,743	678,227
Originated Loans [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	5,255	5,653
> 90 Days Past Due and Still Accruing	536	471
Non- Accrual	1,190	1,060
Total Past Due	6,981	7,184
Current	796,220	642,517
Total Loans	803,201	649,701
Originated Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,581	1,737
> 90 Days Past Due and Still Accruing	646	1,076
Non- Accrual	873	412
Total Past Due	4,100	3,225
Current	910,907	829,443
Total Loans	915,007	832,668
Originated Loans [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	141	25
> 90 Days Past Due and Still Accruing	25	10
Non- Accrual
Total Past Due	166	35
Current	54,095	45,148
Total Loans	54,261	45,183
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	29,191	30,205
> 90 Days Past Due and Still Accruing	39,236	45,823
Non- Accrual		0
Total Past Due	68,427	76,028
Current	1,736,923	1,373,199
Discount	(88,118)	(97,898)
Total Loans	1,717,232	1,351,329
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	14,415	13,637
> 90 Days Past Due and Still Accruing	14,019	20,668
Non- Accrual		0
Total Past Due	28,434	34,305
Current	866,319	619,197
Discount	(34,735)	(48,721)
Total Loans	860,018	604,781
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	350	1,860
> 90 Days Past Due and Still Accruing	2,306	1,899
Non- Accrual		0
Total Past Due	2,656	3,759
Current	147,605	124,415
Discount	(7,215)	(8,368)
Total Loans	143,046	119,806
Acquired Loans [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due		0
> 90 Days Past Due and Still Accruing		0
Non- Accrual		0
Total Past Due		0
Current		0
Discount		0
Total Loans		0
Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	14,765	15,497
> 90 Days Past Due and Still Accruing	16,325	22,567
Non- Accrual		0
Total Past Due	31,090	38,064
Current	1,013,924	743,612
Discount	(41,950)	(57,089)
Total Loans	1,003,064	724,587
Acquired Loans [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,280	1,447
> 90 Days Past Due and Still Accruing	1,399	1,178
Non- Accrual		0
Total Past Due	2,679	2,625
Current	65,972	74,917
Discount	1,565	1,699
Total Loans	70,216	79,241
Acquired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	11,010	11,464
> 90 Days Past Due and Still Accruing	18,573	19,298
Non- Accrual		0
Total Past Due	29,583	30,762
Current	479,330	412,704
Discount	(39,860)	(34,954)
Total Loans	469,053	408,512
Acquired Loans [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	45	205
> 90 Days Past Due and Still Accruing	22	31
Non- Accrual		0
Total Past Due	67	236
Current	2,991	6,267
Discount	(423)	(617)
Total Loans	2,635	5,886
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,091	1,592
> 90 Days Past Due and Still Accruing	2,917	2,749
Non- Accrual		0
Total Past Due	5,008	4,341
Current	174,706	135,699
Discount	(7,450)	(6,937)
Total Loans	172,264	133,103
Acquired Loans [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due
> 90 Days Past Due and Still Accruing		0
Non- Accrual		0
Total Past Due		0
Current		0
Discount		0
Total Loans		$ 0