Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest bearing deposits with banks	$ 1,352,918	$ 1,071,360
Equity securities	32,973	29,378
Total held to maturity debt securities	2,413,361	2,227,612
Accrued interest receivable	107,790	106,230
Deposits with stated maturities	5,451,078	6,714,678
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	74,179	75,484
U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	5,795	6,513
Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	465,674	484,506
Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	1,797,741	1,589,655
Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	30,728	30,033
Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	39,244	41,421
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	2,391,026	2,173,011
Carrying Amount | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and due from banks	280,915	257,845
Interest bearing deposits with banks	1,352,918	1,071,360
Accrued interest receivable	107,790	106,230
Deposits without stated maturities	27,134,131	25,220,924
Short-term borrowings	1,084,666	1,147,958
Accrued interest payable	19,972	18,839
Carrying Amount | Level 1 | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	68,031	68,126
Carrying Amount | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Federal Reserve Bank and Federal Home Loan Bank stock	247,158	250,116
Deposits with stated maturities	5,451,078	6,714,678
Long-term borrowings	2,242,931	2,295,665
Junior subordinated debentures issued to capital trusts	56,152	56,065
Carrying Amount | Level 2 | U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	5,659	6,222
Carrying Amount | Level 2 | Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	454,021	470,259
Carrying Amount | Level 2 | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	1,787,211	1,550,306
Carrying Amount | Level 2 | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	37,354	37,348
Carrying Amount | Level 2 | Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	38,750	40,750
Carrying Amount | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,249	2,999
Net loans	32,343,536	31,876,869
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	2,413,361	2,227,612
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and due from banks	280,915	257,845
Interest bearing deposits with banks	1,352,918	1,071,360
Accrued interest receivable	107,790	106,230
Deposits without stated maturities	27,134,131	25,220,924
Short-term borrowings	1,060,430	1,151,478
Accrued interest payable	19,972	18,839
Fair Value | Level 1 | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	74,179	75,484
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Federal Reserve Bank and Federal Home Loan Bank stock	247,158	250,116
Deposits with stated maturities	5,448,891	6,639,022
Long-term borrowings	2,242,747	2,405,345
Junior subordinated debentures issued to capital trusts	45,863	57,779
Fair Value | Level 2 | U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	5,795	6,513
Fair Value | Level 2 | Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	465,674	484,506
Fair Value | Level 2 | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	1,797,741	1,589,655
Fair Value | Level 2 | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	30,728	30,033
Fair Value | Level 2 | Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	39,244	41,421
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,249	2,999
Net loans	$ 32,113,414	$ 31,635,060