Fair Value Measurements - Fair Values of Corporation's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying amount	$ 270,720	$ 213,981	$ 230,102	$ 239,044
Securities available for sale, carrying amount	1,384,273	1,141,650
Securities held to maturity, carrying amount	1,427,852	1,199,169
Net loans, including loans held for sale, carrying amount	10,219,830	9,402,448
Bank owned life insurance, carrying amount	309,750	289,402
Derivative assets, carrying amount	39,238	33,317
Accrued interest receivable, carrying amount	37,036	35,520
Deposits, carrying amount	11,057,770	10,198,232
Short-term borrowings, carrying amount	1,504,510	1,241,239
Long-term debt, carrying amount	335,854	143,928
Junior subordinated debt, carrying amount	58,220	75,205
Derivative liabilities, carrying amount	42,533	43,369
Accrued interest payable, carrying amount	5,998	7,061
Cash and cash equivalents, fair value	270,720	213,981
Securities available for sale, fair value	1,384,273	1,141,650
Securities held to maturity, fair value	1,439,241	1,189,563
Net loans, including loans held for sale, fair value	10,041,484	9,243,780
Bank owned life insurance, fair value	315,714	292,694
Derivative assets, fair value	39,238	33,317
Accrued interest receivable, fair value	37,036	35,520
Deposits, fair value	11,065,652	10,208,268
Short-term borrowings, fair value	1,504,510	1,241,239
Long-term debt, fair value	338,373	145,995
Junior subordinated debt, fair value	59,156	70,442
Derivative liabilities, fair value	42,533	43,369
Accrued interest payable, fair value	5,998	7,061
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	270,720	213,981
Securities available for sale, fair value	205	649
Securities held to maturity, fair value
Net loans, including loans held for sale, fair value
Bank owned life insurance, fair value	315,714	292,694
Derivative assets, fair value
Accrued interest receivable, fair value	37,036	35,520
Deposits, fair value	8,359,933	7,592,159
Short-term borrowings, fair value	1,504,510	1,241,239
Long-term debt, fair value
Junior subordinated debt, fair value
Derivative liabilities, fair value
Accrued interest payable, fair value	5,998	7,061
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value
Securities available for sale, fair value	1,382,014	1,107,252
Securities held to maturity, fair value	1,433,404	1,182,671
Net loans, including loans held for sale, fair value
Bank owned life insurance, fair value
Derivative assets, fair value	39,238	33,317
Accrued interest receivable, fair value
Deposits, fair value	2,705,719	2,616,109
Short-term borrowings, fair value
Long-term debt, fair value
Junior subordinated debt, fair value
Derivative liabilities, fair value	42,533	43,369
Accrued interest payable, fair value
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value
Securities available for sale, fair value	2,054	33,749
Securities held to maturity, fair value	5,837	6,892
Net loans, including loans held for sale, fair value	10,041,484	9,243,780
Bank owned life insurance, fair value
Derivative assets, fair value
Accrued interest receivable, fair value
Deposits, fair value
Short-term borrowings, fair value
Long-term debt, fair value	338,373	145,995
Junior subordinated debt, fair value	59,156	70,442
Derivative liabilities, fair value
Accrued interest payable, fair value