Loans and Allowance for Loan Losses - Summary of Individual and Collective Allowance for Loan Losses and Loan Balances by Class (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	$ 1,469	$ 824
Allowance, Collectively Evaluated for Impairment	109,719	104,060
Loans	10,333,873	9,506,094
Loans Outstanding, Individually Evaluated for Impairment	34,603	34,376
Loans Outstanding, Collectively Evaluated for Impairment	8,795,476	8,120,389
Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	660	701
Allowance, Collectively Evaluated for Impairment	37,818	31,847
Loans	3,577,933	3,245,209
Loans Outstanding, Individually Evaluated for Impairment	27,909	30,133
Loans Outstanding, Collectively Evaluated for Impairment	2,812,927	2,610,295
Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	809	123
Allowance, Collectively Evaluated for Impairment	32,208	32,480
Loans	2,103,896	1,881,474
Loans Outstanding, Individually Evaluated for Impairment	6,694	4,243
Loans Outstanding, Collectively Evaluated for Impairment	1,990,314	1,757,425
Commercial Leases [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment
Allowance, Collectively Evaluated for Impairment	2,079	1,903
Loans	164,676	158,895
Loans Outstanding, Collectively Evaluated for Impairment	164,676	158,895
Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	1,469	824
Allowance, Collectively Evaluated for Impairment	72,105	66,230
Loans	5,846,505	5,285,578
Loans Outstanding, Individually Evaluated for Impairment	34,603	34,376
Loans Outstanding, Collectively Evaluated for Impairment	4,967,917	4,526,615
Direct Installment [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	16,844	17,824
Loans	1,512,149	1,467,236
Loans Outstanding, Collectively Evaluated for Impairment	1,438,347	1,387,995
Residential Mortgages [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	5,506	5,836
Loans	1,145,286	1,086,739
Loans Outstanding, Collectively Evaluated for Impairment	718,332	678,227
Indirect Installment [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	6,693	6,409
Loans	729,513	655,587
Loans Outstanding, Collectively Evaluated for Impairment	726,066	649,701
Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	7,664	7,231
Loans	1,037,519	965,771
Loans Outstanding, Collectively Evaluated for Impairment	881,913	832,668
Other [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	907	530
Loans	62,901	45,183
Loans Outstanding, Collectively Evaluated for Impairment	62,901	45,183
Originated Loans [Member]
Valuation Allowance [Line Items]
Loans	8,830,079	8,154,765
Originated Loans [Member] | Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Loans	2,840,836	2,640,428
Originated Loans [Member] | Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Loans	1,997,008	1,761,668
Originated Loans [Member] | Commercial Leases [Member]
Valuation Allowance [Line Items]
Loans	164,676	158,895
Originated Loans [Member] | Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Loans	5,002,520	4,560,991
Originated Loans [Member] | Direct Installment [Member]
Valuation Allowance [Line Items]
Loans	1,438,347	1,387,995
Originated Loans [Member] | Residential Mortgages [Member]
Valuation Allowance [Line Items]
Loans	718,332	678,227
Originated Loans [Member] | Indirect Installment [Member]
Valuation Allowance [Line Items]
Loans	726,066	649,701
Originated Loans [Member] | Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Loans	881,913	832,668
Originated Loans [Member] | Other [Member]
Valuation Allowance [Line Items]
Loans	$ 62,901	$ 45,183