Investment Securities - Amortized Cost of Debt Securities Held to Maturity by External Credit Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	$ 3,541,456	$ 3,532,220
U.S. Treasury securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities		25,480
U.S. government agency securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	292,897	301,315
Obligations of states and state agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	62,184	68,025
Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	287,789	304,464
Obligations of states and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	349,973	372,489
Residential mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	2,777,381	2,710,642
Trust preferred securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	36,097	36,081
Corporate and other debt securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	85,108	86,213
AAA/AA/A Rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	3,359,926	3,368,128
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		25,480
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	292,897	301,315
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	48,366	52,770
AAA/AA/A Rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	241,282	277,921
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	289,648	330,691
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	2,777,381	2,710,642
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	0
BBB rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	3,000	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
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	3,000	6,000
Non-rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	178,530	158,092
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
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	13,818	15,255
Non-rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	46,507	26,543
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	60,325	41,798
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	36,097	36,081
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	$ 82,108	$ 80,213