Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
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	$ 160,462	$ 170,225
Total investment securities held to maturity	1,891,982	1,621,039
Accrued interest receivable	63,815	63,554
Deposits with stated maturities	3,119,881	3,157,904
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	1,845,151	1,596,385
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	238,664	243,575
Interest bearing deposits with banks	160,462	170,225
Accrued interest receivable	63,815	63,554
Federal Reserve Bank and Federal Home Loan Bank stock	162,584	145,068
Deposits without stated maturities	13,852,302	13,095,647
Short-term borrowings	1,433,356	1,076,991
Accrued interest payable	9,931	13,110
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	138,866	138,978
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	3,119,881	3,157,904
Long-term borrowings	1,450,818	1,810,728
Junior subordinated debentures issued to capital trusts	41,536	41,414
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	11,549	12,859
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	568,212	504,865
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	1,030,165	852,289
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	59,800	59,785
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	36,559	27,609
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	16,523,438	15,936,929
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	1,891,982	1,621,039
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	238,664	243,575
Interest bearing deposits with banks	160,462	170,225
Accrued interest receivable	63,815	63,554
Federal Reserve Bank and Federal Home Loan Bank stock	162,584	145,068
Deposits without stated maturities	13,852,302	13,095,647
Short-term borrowings	1,433,356	1,076,991
Accrued interest payable	9,931	13,110
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	154,042	149,483
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	3,148,902	3,203,389
Long-term borrowings	1,612,654	1,945,741
Junior subordinated debentures issued to capital trusts	43,751	44,127
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	12,106	13,130
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	595,525	527,263
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	1,046,387	855,272
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	45,726	46,437
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	38,196	29,454
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	$ 16,511,137	$ 15,824,475