Fair Value Disclosures (Carrying Amounts and Estimated Fair Values) (Detail) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	$ 456,917,000	$ 305,357,000
Investment securities	2,183,093,000	2,375,224,000
Restricted investment in bank stocks	141,689,000	158,232,000
Loans and leases	13,522,670,000	13,418,478,000
Derivatives	24,586,000	24,316,000
Deposits	13,314,994,000	12,869,372,000
Derivatives	43,164,000	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	456,917,000	305,357,000
Short-term investments	0	0
Investment securities	21,479,000	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	78,849,000	83,227,000
Investment securities	2,146,816,000	2,340,235,000
Restricted investment in bank stocks	141,689,000	158,232,000
Loans and leases	0	0
Derivatives	24,586,000	24,316,000
Deposits	12,472,338,000	11,901,099,000
Short-term borrowings	527,079,000	555,740,000
FHLB borrowings	1,131,404,000	1,531,606,000
Long-term debt	361,178,000	461,247,000
Derivatives	43,164,000	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	14,798,000	14,094,000
Restricted investment in bank stocks	0	0
Loans and leases	13,678,712,000	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	456,917,000	305,357,000
Short-term investments	78,849,000	83,227,000
Investment securities	2,183,093,000	2,375,224,000
Restricted investment in bank stocks	141,689,000	158,232,000
Loans and leases	13,667,153,000	13,576,086,000
Derivatives	24,586,000	24,316,000
Deposits	13,314,994,000	12,869,372,000
Short-term borrowings	527,079,000	555,740,000
FHLB borrowings	1,127,302,000	1,531,282,000
Long-term debt	360,033,000	453,260,000
Derivatives	43,164,000	50,247,000
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and due from banks	456,917,000	305,357,000
Short-term investments	78,849,000	83,227,000
Investment securities	2,183,093,000	2,375,224,000
Restricted investment in bank stocks	141,689,000	158,232,000
Loans and leases	13,678,712,000	13,463,676,000
Derivatives	24,586,000	24,316,000
Deposits	12,472,338,000	11,901,099,000
Short-term borrowings	527,079,000	555,740,000
FHLB borrowings	1,131,404,000	1,531,606,000
Long-term debt	361,178,000	461,247,000
Derivatives	$ 43,164,000	$ 50,247,000