Fair Value Disclosures (Carrying Amounts and Estimated Fair Values) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 380,100	$ 276,384
Restricted investment in bank stocks	144,927	128,073
Loans and leases	12,488,710	10,259,830
Deposits	12,725,379	10,290,472
Short-term borrowings	762,257	613,306
Derivatives	79,276	73,161
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	307,642	179,615
Short-term investments	0	0
Investment securities	1,382	221
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	72,458	96,769
Short-term investments	104,608	121,686
Investment securities	2,746,456	2,278,090
Restricted investment in bank stocks	144,927	128,073
Loans and leases	0	0
Derivatives	28,739	26,463
Deposits	12,710,035	9,953,598
Short-term borrowings	762,257	613,306
FHLB borrowings	1,102,130	967,163
Long-term debt	625,573	622,167
Derivatives	79,276	73,161
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	15,639	16,723
Restricted investment in bank stocks	0	0
Loans and leases	12,738,562	10,344,966
Derivatives	0	0
Deposits	0	0
Short-term borrowings	0	0
FHLB borrowings	0	0
Long-term debt	0	0
Derivatives	0	0
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	380,100	276,384
Short-term investments	104,608	121,686
Investment securities	2,763,477	2,295,034
Restricted investment in bank stocks	144,927	128,073
Loans and leases	12,675,607	10,259,830
Derivatives	28,739	26,463
Deposits	12,725,379	10,290,472
Short-term borrowings	762,257	613,306
FHLB borrowings	1,110,884	971,020
Long-term debt	639,753	656,726
Derivatives	79,276	73,161
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	380,100	276,384
Short-term investments	104,608	121,686
Investment securities	2,763,477	2,295,034
Restricted investment in bank stocks	144,927	128,073
Loans and leases	12,738,562	10,344,966
Derivatives	28,739	26,463
Deposits	12,710,035	9,953,598
Short-term borrowings	762,257	613,306
FHLB borrowings	1,102,130	967,163
Long-term debt	625,573	622,167
Derivatives	$ 79,276	$ 73,161