Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Interest bearing deposits with banks	$ 71,756	$ 367,838
Total investment securities held to maturity	1,670,951	1,815,976
Accrued interest receivable	57,532	57,333
Deposits with stated maturities	3,154,641	2,742,468
Carrying Amount
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	1,637,310	1,778,316
Carrying Amount | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Cash and due from banks	220,023	462,569
Interest bearing deposits with banks	71,756	367,838
Accrued interest receivable	57,532	57,333
Federal Reserve Bank and Federal Home Loan Bank stock	137,229	133,117
Deposits without stated maturities	11,345,222	11,291,648
Short-term borrowings	302,941	146,781
Accrued interest payable	12,825	15,526
Carrying Amount | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	139,014	139,121
Carrying Amount | Significant Other Observable Inputs (Level 2)
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Deposits with stated maturities	3,154,641	2,742,468
Long-term borrowings	2,529,326	2,526,408
Junior subordinated debentures issued to capital trusts	41,374	41,252
Carrying Amount | Significant Other Observable Inputs (Level 2) | U.S. government agency securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	12,973	14,081
Carrying Amount | Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	511,788	500,018
Carrying Amount | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	889,146	986,992
Carrying Amount | Significant Other Observable Inputs (Level 2) | Trust preferred securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	59,780	98,456
Carrying Amount | Significant Other Observable Inputs (Level 2) | Corporate and other debt securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	24,609	39,648
Carrying Amount | Significant Unobservable Inputs (Level 3)
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Net loans	14,912,263	13,371,560
Fair Value
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	1,670,951	1,815,976
Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Cash and due from banks	220,023	462,569
Interest bearing deposits with banks	71,756	367,838
Accrued interest receivable	57,532	57,333
Federal Reserve Bank and Federal Home Loan Bank stock	137,229	133,117
Deposits without stated maturities	11,345,222	11,291,648
Short-term borrowings	302,941	146,781
Accrued interest payable	12,825	15,526
Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	152,513	151,300
Fair Value | Significant Other Observable Inputs (Level 2)
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Deposits with stated maturities	3,202,590	2,807,522
Long-term borrowings	2,696,964	2,738,122
Junior subordinated debentures issued to capital trusts	43,950	44,584
Fair Value | Significant Other Observable Inputs (Level 2) | U.S. government agency securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	13,400	14,385
Fair Value | Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	531,616	519,693
Fair Value | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	899,776	998,981
Fair Value | Significant Other Observable Inputs (Level 2) | Trust preferred securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	46,811	86,243
Fair Value | Significant Other Observable Inputs (Level 2) | Corporate and other debt securities
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Total investment securities held to maturity	26,835	45,374
Fair Value | Significant Unobservable Inputs (Level 3)
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Net loans	$ 14,633,265	$ 13,085,830