Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest bearing deposits with banks	$ 1,515,757	$ 1,071,360
Equity securities	33,870	29,378
Total held to maturity debt securities	2,556,519	2,227,612
Accrued interest receivable	99,068	106,230
Deposits with stated maturities	4,307,549	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	73,575	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	5,813	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	454,718	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	1,938,608	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	31,425	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	52,380	41,421
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	2,533,812	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	329,006	257,845
Interest bearing deposits with banks	1,515,757	1,071,360
Accrued interest receivable	99,068	106,230
Deposits without stated maturities	28,887,225	25,220,924
Short-term borrowings	854,378	1,147,958
Accrued interest payable	8,115	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	67,874	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	212,122	250,116
Deposits with stated maturities	4,307,549	6,714,678
Long-term borrowings	1,885,690	2,295,665
Junior subordinated debentures issued to capital trusts	56,239	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	5,548	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	444,380	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	1,926,900	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	37,360	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	51,750	40,750
Carrying Amount | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,513	2,999
Net loans	32,118,130	31,876,869
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total held to maturity debt securities	2,556,519	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	329,006	257,845
Interest bearing deposits with banks	1,515,757	1,071,360
Accrued interest receivable	99,068	106,230
Deposits without stated maturities	28,887,225	25,220,924
Short-term borrowings	838,440	1,151,478
Accrued interest payable	8,115	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	73,575	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	212,122	250,116
Deposits with stated maturities	4,256,745	6,639,022
Long-term borrowings	1,882,750	2,405,345
Junior subordinated debentures issued to capital trusts	45,802	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	5,813	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	454,718	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	1,938,608	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	31,425	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	52,380	41,421
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,513	2,999
Net loans	$ 31,962,961	$ 31,635,060