Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
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	$ 128,226	$ 171,710
Investment securities held to maturity:	1,831,145	1,924,597
Accrued interest receivable	72,063	66,816
Deposits with stated maturities	3,420,656	3,138,871
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
Investment securities held to maturity:	1,823,622	1,925,572
Carrying Amount | 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	215,600	220,791
Interest bearing deposits with banks	128,226	171,710
Accrued interest receivable	72,063	66,816
Federal Reserve Bank and Federal Home Loan Bank stock	204,978	147,127
Deposits without stated maturities	13,892,110	14,591,837
Short-term borrowings	1,482,709	1,080,960
Accrued interest payable	10,812	10,675
Carrying Amount | 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
Investment securities held to maturity:	138,714	138,830
Carrying Amount | 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	3,420,656	3,138,871
Long-term borrowings	2,215,219	1,433,906
Junior subordinated debentures issued to capital trusts	41,716	41,577
Carrying Amount | 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
Investment securities held to maturity:	9,984	11,329
Carrying Amount | 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
Investment securities held to maturity:	495,157	566,590
Carrying Amount | 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
Investment securities held to maturity:	1,088,389	1,112,460
Carrying Amount | 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
Investment securities held to maturity:	49,819	59,804
Carrying Amount | 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
Investment securities held to maturity:	41,559	36,559
Carrying Amount | 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	18,082,496	17,121,684
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
Investment securities held to maturity:	1,831,145	1,924,597
Fair Value | 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	215,600	220,791
Interest bearing deposits with banks	128,226	171,710
Accrued interest receivable	72,063	66,816
Federal Reserve Bank and Federal Home Loan Bank stock	204,978	147,127
Deposits without stated maturities	13,892,110	14,591,837
Short-term borrowings	1,485,695	1,081,751
Accrued interest payable	10,812	10,675
Fair Value | 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
Investment securities held to maturity:	147,126	147,495
Fair Value | 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	3,436,229	3,160,572
Long-term borrowings	2,300,388	1,523,386
Junior subordinated debentures issued to capital trusts	42,244	45,785
Fair Value | 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
Investment securities held to maturity:	10,188	11,464
Fair Value | 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
Investment securities held to maturity:	511,159	577,826
Fair Value | 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
Investment securities held to maturity:	1,081,703	1,102,802
Fair Value | 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
Investment securities held to maturity:	38,998	47,290
Fair Value | 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
Investment securities held to maturity:	41,971	37,720
Fair Value | 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	$ 17,741,813	$ 16,756,655