Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 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	$ 40,580	$ 134,915
Total investment securities held to maturity	1,854,121	1,711,427
Accrued interest receivable	53,650	53,964
Time	2,191,489	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	1,826,143	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	266,101	234,253
Interest bearing deposits with banks	40,580	134,915
Accrued interest receivable	53,650	53,964
Federal Reserve Bank and Federal Home Loan Bank stock	138,180	137,234
Deposits without stated maturities	9,224,563	9,139,993
Short-term borrowings	354,230	281,455
Accrued interest payable	16,652	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	139,192	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	2,191,489	2,179,269
Long-term borrowings	2,797,986	2,792,306
Junior subordinated debentures issued to capital trusts	41,171	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	14,346	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	515,402	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	1,019,086	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	98,452	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	39,665	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	11,710,375	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	1,854,121	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	266,101	234,253
Interest bearing deposits with banks	40,580	134,915
Accrued interest receivable	53,650	53,964
Federal Reserve Bank and Federal Home Loan Bank stock	138,180	137,234
Deposits without stated maturities	9,224,563	9,139,993
Short-term borrowings	354,230	281,455
Accrued interest payable	16,652	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	149,128	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	2,254,453	2,206,427
Long-term borrowings	3,040,487	3,036,953
Junior subordinated debentures issued to capital trusts	45,191	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	14,718	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	530,393	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	1,028,120	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	85,886	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	45,876	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	$ 11,513,205	$ 11,294,348