Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 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	$ 233,228	$ 170,225
Total investment securities held to maturity	1,660,224	1,621,039
Accrued interest receivable	62,973	63,554
Deposits with stated maturities	3,081,012	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	1,618,466	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	243,265	243,575
Interest bearing deposits with banks	233,228	170,225
Accrued interest receivable	62,973	63,554
Federal Reserve Bank and Federal Home Loan Bank stock	145,699	145,068
Deposits without stated maturities	13,327,414	13,095,647
Short-term borrowings	1,170,623	1,076,991
Accrued interest payable	11,789	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	138,942	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	3,081,012	3,157,904
Long-term borrowings	1,660,284	1,810,728
Junior subordinated debentures issued to capital trusts	41,455	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	12,225	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	516,645	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	859,305	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	59,790	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	31,559	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	16,030,572	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	1,660,224	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	243,265	243,575
Interest bearing deposits with banks	233,228	170,225
Accrued interest receivable	62,973	63,554
Federal Reserve Bank and Federal Home Loan Bank stock	145,699	145,068
Deposits without stated maturities	13,327,414	13,095,647
Short-term borrowings	1,170,623	1,076,991
Accrued interest payable	11,789	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	153,877	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	3,122,098	3,203,389
Long-term borrowings	1,823,824	1,945,741
Junior subordinated debentures issued to capital trusts	43,797	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	12,738	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	543,069	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	870,711	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	46,404	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	33,425	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	$ 16,008,152	$ 15,824,475