Fair Value Disclosures (Carrying Amounts and Estimated Fair Values) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	$ 367,902	$ 277,042
Restricted investment in bank stocks	150,749	152,434
Loans and leases	12,979,168	12,710,721
Deposits	12,764,232	12,580,046
Derivatives	58,146	72,126
Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	367,902	277,042
Short-term investments	81,456	119,176
Investment securities	2,343,429	2,577,901
Restricted investment in bank stocks	150,749	152,434
Loans and leases	13,157,762	12,894,741
Derivatives	27,607	25,915
Deposits	12,764,232	12,580,046
Short-term borrowings	706,065	817,577
FHLB borrowings	1,161,995	1,199,062
Long-term debt	489,002	513,401
Derivatives	58,146	72,126
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	367,902	277,042
Short-term investments	81,456	119,176
Investment securities	2,343,429	2,577,901
Restricted investment in bank stocks	150,749	152,434
Loans and leases	13,276,903	12,954,918
Derivatives	27,607	25,915
Deposits	12,750,862	12,544,069
Short-term borrowings	706,065	817,577
FHLB borrowings	1,162,217	1,200,358
Long-term debt	488,894	512,632
Derivatives	58,146	72,126
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	367,902	277,042
Short-term investments	0	0
Investment securities	20,834	21,266
Restricted investment in bank stocks	0	0
Loans and leases	0	0
Derivatives	0	0
Deposits	0	0
Short-term borrowings	0	0
FHLB borrowings	0	0
Long-term debt	0	0
Derivatives	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	0	0
Short-term investments	81,456	119,176
Investment securities	2,284,720	2,517,129
Restricted investment in bank stocks	150,749	152,434
Loans and leases	0	0
Derivatives	27,607	25,915
Deposits	12,750,862	12,544,069
Short-term borrowings	706,065	817,577
FHLB borrowings	1,162,217	1,200,358
Long-term debt	488,894	512,632
Derivatives	58,146	72,126
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	0	0
Short-term investments	0	0
Investment securities	37,875	39,506
Restricted investment in bank stocks	0	0
Loans and leases	13,276,903	12,954,918
Derivatives	0	0
Deposits	0	0
Short-term borrowings	0	0
FHLB borrowings	0	0
Long-term debt	0	0
Derivatives	$ 0	$ 0