Fair Value Disclosures (Carrying Amounts and Estimated Fair Values) (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	$ 772,677,000	$ 305,357,000
Investment securities	2,192,615,000	2,375,224,000
Restricted investment in bank stocks	133,119,000	158,232,000
Loans and leases	13,361,516,000	13,503,392,000
Derivatives	22,339,000	24,316,000
Deposits	13,588,524,000	12,869,372,000
Derivatives	35,668,000	50,247,000
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	772,677,000	305,357,000
Short-term investments	0	0
Investment securities	21,665,000	20,895,000
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	79,662,000	83,227,000
Investment securities	2,156,420,000	2,340,235,000
Restricted investment in bank stocks	133,119,000	158,232,000
Loans and leases	0	0
Derivatives	22,339,000	24,316,000
Deposits	12,660,047,000	11,901,099,000
Short-term borrowings	532,675,000	555,740,000
FHLB borrowings	918,764,000	1,531,606,000
Long-term debt	354,524,000	461,247,000
Derivatives	35,668,000	50,247,000
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	14,530,000	14,094,000
Restricted investment in bank stocks	0	0
Loans and leases	13,422,747,000	13,463,676,000
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	772,677,000	305,357,000
Short-term investments	79,662,000	83,227,000
Investment securities	2,192,615,000	2,375,224,000
Restricted investment in bank stocks	133,119,000	158,232,000
Loans and leases	13,425,721,000	13,576,086,000
Derivatives	22,339,000	24,316,000
Deposits	13,588,524,000	12,869,372,000
Short-term borrowings	532,675,000	555,740,000
FHLB borrowings	915,362,000	1,531,282,000
Long-term debt	356,117,000	453,260,000
Derivatives	35,668,000	50,247,000
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	772,677,000	305,357,000
Short-term investments	79,662,000	83,227,000
Investment securities	2,192,615,000	2,375,224,000
Restricted investment in bank stocks	133,119,000	158,232,000
Loans and leases	13,422,747,000	13,463,676,000
Derivatives	22,339,000	24,316,000
Deposits	12,660,047,000	11,901,099,000
Short-term borrowings	532,675,000	555,740,000
FHLB borrowings	918,764,000	1,531,606,000
Long-term debt	354,524,000	461,247,000
Derivatives	$ 35,668,000	$ 50,247,000