Fair Value Measurements - Fair Values of Corporation's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 230,102	$ 239,044	$ 222,758	$ 208,953
Securities available for sale	1,164,903	1,172,683
Securities held to maturity	1,149,481	1,106,563
Bank owned life insurance	262,877	246,088
Derivative assets	37,638	58,008
Deposits	9,646,198	9,082,174
Short-term borrowings	1,030,617	1,083,138
Long-term debt	92,420	89,425
Junior subordinated debt	194,200	204,019
Derivative liabilities	44,422	58,150
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	664	396
Derivative assets
Derivative liabilities
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	1,128,715	1,139,722
Derivative assets	37,638	58,008
Derivative liabilities	44,422	58,150
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available for sale	35,524	32,565
Derivative assets
Derivative liabilities
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	230,102	239,044
Securities available for sale	1,164,903	1,172,683
Securities held to maturity	1,149,481	1,106,563
Net loans, including loans held for sale	8,548,423	8,061,096
Bank owned life insurance	262,877	246,088
Derivative assets	37,638	58,008
Accrued interest receivable	32,664	30,210
Deposits	9,646,198	9,082,174
Short-term borrowings	1,030,617	1,083,138
Long-term debt	92,420	89,425
Junior subordinated debt	194,200	204,019
Derivative liabilities	44,422	58,150
Accrued interest payable	7,044	9,054
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	230,102	239,044
Securities available for sale	1,164,903	1,172,683
Securities held to maturity	1,153,077	1,143,213
Net loans, including loans held for sale	8,429,458	7,996,554
Bank owned life insurance	268,353	257,060
Derivative assets	37,638	58,008
Accrued interest receivable	32,664	30,210
Deposits	9,660,801	9,117,757
Short-term borrowings	1,030,617	1,083,138
Long-term debt	94,415	92,329
Junior subordinated debt	186,350	172,246
Derivative liabilities	44,422	58,150
Accrued interest payable	7,044	9,054
Fair Value [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	230,102	239,044
Securities available for sale	664	396
Securities held to maturity
Net loans, including loans held for sale
Bank owned life insurance	268,353	257,060
Derivative assets
Accrued interest receivable	32,664	30,210
Deposits	7,218,161	6,546,316
Short-term borrowings	1,030,617	1,083,138
Long-term debt
Junior subordinated debt
Derivative liabilities
Accrued interest payable	7,044	9,054
Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents
Securities available for sale	1,128,715	1,139,722
Securities held to maturity	1,144,994	1,128,524
Net loans, including loans held for sale
Bank owned life insurance
Derivative assets	37,638	58,008
Accrued interest receivable
Deposits	2,442,640	2,571,441
Short-term borrowings
Long-term debt
Junior subordinated debt
Derivative liabilities	44,422	58,150
Accrued interest payable
Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents
Securities available for sale	35,524	32,565
Securities held to maturity	8,083	14,689
Net loans, including loans held for sale	8,429,458	7,966,554
Bank owned life insurance
Derivative assets
Accrued interest receivable
Deposits
Short-term borrowings
Long-term debt	94,415	92,329
Junior subordinated debt	186,350	172,246
Derivative liabilities
Accrued interest payable