Investment Securities - Amortized Cost of Debt Securities Held to Maturity by External Credit Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	$ 3,073,205	$ 2,668,697
U.S. Treasury securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	67,401	67,558
U.S. government agency securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	5,572	6,265
Obligations of states and state agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	132,017	141,015
Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	187,143	196,947
Obligations of states and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	319,160	337,962
Residential mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	2,594,295	2,166,142
Trust preferred securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	37,027	37,020
Corporate and other debt securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	49,750	53,750
AAA/AA/A Rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	2,915,441	2,509,187
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	67,401	67,558
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	5,572	6,265
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	110,710	118,368
AAA/AA/A Rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	135,463	148,854
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	246,173	267,222
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	2,594,295	2,166,142
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	2,000	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	5,556	5,576
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	5,556	5,576
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	5,556	5,576
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	146,208	147,934
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	15,751	17,071
Non-rated | Municipal bonds
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized cost of held to maturity debt securities	51,680	48,093
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	67,431	65,164
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	37,027	37,020
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	$ 41,750	$ 45,750