Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest bearing deposits with banks	$ 718,260,000	$ 178,423,000
Equity securities	49,701,000	41,410,000
Total investment securities held to maturity	2,382,938,000	2,358,720,000
Accrued interest receivable	107,353,000	105,637,000
Deposits with stated maturities	8,567,085,000	9,717,945,000
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	2,317,033,000	2,336,095,000
Carrying Amount | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and due from banks	286,755,000	256,264,000
Interest bearing deposits with banks	718,260,000	178,423,000
Accrued interest receivable	107,353,000	105,637,000
Federal Reserve Bank and Federal Home Loan Bank stock	295,420,000	214,421,000
Deposits without stated maturities	20,449,903,000	19,467,892,000
Short-term borrowings	2,095,655,000	1,093,280,000
Accrued interest payable	26,724,000	33,066,000
Carrying Amount | Level 1 | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	138,311,000	138,352,000
Carrying Amount | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with stated maturities	8,567,085,000	9,717,945,000
Long-term borrowings	2,805,639,000	2,122,426,000
Junior subordinated debentures issued to capital trusts	55,805,000	55,718,000
Carrying Amount | Level 2 | U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	6,794,000	7,345,000
Carrying Amount | Level 2 | Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	480,698,000	500,705,000
Carrying Amount | Level 2 | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	1,616,150,000	1,620,119,000
Carrying Amount | Level 2 | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	37,330,000	37,324,000
Carrying Amount | Level 2 | Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	37,750,000	32,250,000
Carrying Amount | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	30,144,725,000	29,537,449,000
Carrying Amount | NAV
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,000,000	0
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	2,382,938,000	2,358,720,000
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and due from banks	286,755,000	256,264,000
Interest bearing deposits with banks	718,260,000	178,423,000
Accrued interest receivable	107,353,000	105,637,000
Federal Reserve Bank and Federal Home Loan Bank stock	295,420,000	214,421,000
Deposits without stated maturities	20,449,903,000	19,467,892,000
Short-term borrowings	1,952,248,000	1,081,879,000
Accrued interest payable	26,724,000	33,066,000
Fair Value | Level 1 | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	148,124,000	144,113,000
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with stated maturities	8,623,519,000	9,747,867,000
Long-term borrowings	3,060,203,000	2,181,401,000
Junior subordinated debentures issued to capital trusts	64,088,000	53,889,000
Fair Value | Level 2 | U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	6,920,000	7,362,000
Fair Value | Level 2 | Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	492,221,000	513,607,000
Fair Value | Level 2 | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	1,667,403,000	1,629,572,000
Fair Value | Level 2 | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	30,133,000	31,382,000
Fair Value | Level 2 | Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment securities held to maturity	38,137,000	32,684,000
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	29,927,130,000	28,964,396,000
Fair Value | NAV
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	$ 3,000,000	$ 0