Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
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	$ 60,655	$ 134,915
Total investment securities held to maturity	1,838,632	1,711,427
Accrued interest receivable	53,545	53,964
Time	2,183,328	2,179,269
Carrying Amount [Member]
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	1,813,312	1,731,737
Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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	352,799	234,253
Interest bearing deposits with banks	60,655	134,915
Accrued interest receivable	53,545	53,964
Federal Reserve Bank and Federal Home Loan Bank stock	133,586	137,234
Deposits without stated maturities	9,678,159	9,139,993
Short-term borrowings	297,719	281,455
Accrued interest payable	13,959	16,442
Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Securities [Member]
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	139,156	139,255
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Time	2,183,328	2,179,269
Long-term borrowings	2,797,828	2,792,306
Junior subordinated debentures issued to capital trusts	41,211	41,089
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agency Securities [Member]
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	13,881	4,427
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member]
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	501,312	545,886
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage-Backed Securities [Member]
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	1,020,852	886,043
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Trust Preferred Securities [Member]
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	98,454	103,458
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate and Other Debt Securities [Member]
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	39,657	52,668
Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
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	12,062,939	11,453,995
Fair Value [Member]
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	1,838,632	1,711,427
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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	352,799	234,253
Interest bearing deposits with banks	60,655	134,915
Accrued interest receivable	53,545	53,964
Federal Reserve Bank and Federal Home Loan Bank stock	133,586	137,234
Deposits without stated maturities	9,678,159	9,139,993
Short-term borrowings	297,719	281,455
Accrued interest payable	13,959	16,442
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Securities [Member]
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	148,485	144,307
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair value and carrying amounts of assets and liabilities not measured and not reported at fair value on the consolidated statement of financial condition
Time	2,245,962	2,206,427
Long-term borrowings	3,019,564	3,036,953
Junior subordinated debentures issued to capital trusts	46,064	45,261
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agency Securities [Member]
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	14,207	4,365
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member]
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	519,755	543,151
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage-Backed Securities [Member]
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	1,024,402	871,021
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Trust Preferred Securities [Member]
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	86,474	91,489
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate and Other Debt Securities [Member]
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	45,309	57,094
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
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	$ 11,826,631	$ 11,294,348