Investment Securities - Amortized Cost of Debt Securities Held to Maturity by External Credit Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	$ 3,798,709	$ 3,828,984
U.S. Treasury securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	66,408	66,911
U.S. government agency securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	306,339	260,392
Obligations of states and state agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	86,968	99,238
Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	350,673	381,060
Obligations of states and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	437,641	480,298
Residential mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	2,875,630	2,909,106
Trust preferred securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	37,057	37,043
Corporate and other debt securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	75,634	75,234
AAA/AA/A Rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	3,614,070	3,646,840
AAA/AA/A Rated | U.S. Treasury securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	66,408	66,911
AAA/AA/A Rated | U.S. government agency securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	306,339	260,392
AAA/AA/A Rated | Obligations of states and state agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	64,595	74,943
AAA/AA/A Rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	301,098	333,488
AAA/AA/A Rated | Obligations of states and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	365,693	408,431
AAA/AA/A Rated | Residential mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	2,875,630	2,909,106
AAA/AA/A Rated | Trust preferred securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
AAA/AA/A Rated | Corporate and other debt securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	2,000
BBB rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	6,000	6,000
BBB rated | U.S. Treasury securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
BBB rated | U.S. government agency securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
BBB rated | Obligations of states and state agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
BBB rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
BBB rated | Obligations of states and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
BBB rated | Residential mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
BBB rated | Trust preferred securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
BBB rated | Corporate and other debt securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	6,000	6,000
Non-investment grade rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	5,351	5,497
Non-investment grade rated | U.S. Treasury securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-investment grade rated | U.S. government agency securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-investment grade rated | Obligations of states and state agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	5,351	5,497
Non-investment grade rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-investment grade rated | Obligations of states and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	5,351	5,497
Non-investment grade rated | Residential mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-investment grade rated | Trust preferred securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-investment grade rated | Corporate and other debt securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	173,288	170,647
Non-rated | U.S. Treasury securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-rated | U.S. government agency securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-rated | Obligations of states and state agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	17,022	18,798
Non-rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	49,575	47,572
Non-rated | Obligations of states and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	66,597	66,370
Non-rated | Residential mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	0	0
Non-rated | Trust preferred securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	37,057	37,043
Non-rated | Corporate and other debt securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	$ 69,634	$ 67,234