Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
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	$ 274,349	$ 172,800
Investment securities held to maturity:	2,014,954	1,837,620
Accrued interest receivable	86,804	73,990
Deposits with stated maturities	4,757,801	3,563,521
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:	2,048,583	1,842,691
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	222,311	243,310
Interest bearing deposits with banks	274,349	172,800
Accrued interest receivable	86,804	73,990
Federal Reserve Bank and Federal Home Loan Bank stock	227,361	178,668
Deposits without stated maturities	17,202,045	14,589,941
Short-term borrowings	1,618,416	748,628
Accrued interest payable	15,177	14,161
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:	138,638	138,676
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	4,757,801	3,563,521
Long-term borrowings	2,353,548	2,315,819
Junior subordinated debentures issued to capital trusts	55,109	41,774
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:	9,580	9,859
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:	619,271	465,878
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:	1,184,757	1,131,945
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:	49,828	49,824
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:	46,509	46,509
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	22,419,905	18,210,724
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:	2,014,954	1,837,620
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	222,311	243,310
Interest bearing deposits with banks	274,349	172,800
Accrued interest receivable	86,804	73,990
Federal Reserve Bank and Federal Home Loan Bank stock	227,361	178,668
Deposits without stated maturities	17,202,045	14,589,941
Short-term borrowings	1,050,044	679,316
Accrued interest payable	15,177	14,161
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:	142,731	145,257
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	4,464,561	3,465,373
Long-term borrowings	2,298,069	2,453,797
Junior subordinated debentures issued to capital trusts	55,899	37,289
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:	9,437	9,981
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:	622,491	477,479
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:	1,151,067	1,118,044
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:	42,790	40,088
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:	46,438	46,771
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	$ 21,819,997	$ 17,562,153