Fair Value Disclosures (Carrying Amounts and Estimated Fair Values) (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	$ 377,730,000	$ 277,042,000
Investment securities	2,483,375,000	2,577,901,000
Restricted investment in bank stocks	160,787,000	152,434,000
Loans and leases	13,209,714,000	12,710,721,000
Derivatives	22,936,000	25,915,000
Deposits	12,721,685,000	12,580,046,000
Derivatives	54,712,000	72,126,000
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	377,730,000	277,042,000
Short-term investments	0	0
Investment securities	20,912,000	21,266,000
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	77,729,000	119,176,000
Investment securities	2,425,176,000	2,517,129,000
Restricted investment in bank stocks	160,787,000	152,434,000
Loans and leases	0	0
Derivatives	22,936,000	25,915,000
Deposits	12,702,818,000	12,544,069,000
Short-term borrowings	688,456,000	817,577,000
FHLB borrowings	1,593,362,000	1,200,358,000
Long-term debt	463,940,000	512,632,000
Derivatives	54,712,000	72,126,000
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	37,287,000	39,506,000
Restricted investment in bank stocks	0	0
Loans and leases	13,477,467,000	12,954,918,000
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	377,730,000	277,042,000
Short-term investments	77,729,000	119,176,000
Investment securities	2,483,375,000	2,577,901,000
Restricted investment in bank stocks	160,787,000	152,434,000
Loans and leases	13,376,454,000	12,894,741,000
Derivatives	22,936,000	25,915,000
Deposits	12,721,685,000	12,580,046,000
Short-term borrowings	688,456,000	817,577,000
FHLB borrowings	1,593,272,000	1,199,062,000
Long-term debt	457,804,000	513,401,000
Derivatives	54,712,000	72,126,000
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	377,730,000	277,042,000
Short-term investments	77,729,000	119,176,000
Investment securities	2,483,375,000	2,577,901,000
Restricted investment in bank stocks	160,787,000	152,434,000
Loans and leases	13,477,467,000	12,954,918,000
Derivatives	22,936,000	25,915,000
Deposits	12,702,818,000	12,544,069,000
Short-term borrowings	688,456,000	817,577,000
FHLB borrowings	1,593,362,000	1,200,358,000
Long-term debt	463,940,000	512,632,000
Derivatives	$ 54,712,000	$ 72,126,000