Debt Securities - Credit Quality Indictors for HTM Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	$ 3,553,805	$ 3,715,052
State and local governments
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	1,657,628	1,682,640
Investment Grade | Moody's: Aaa | S&P: AAA | State and local governments
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	429,432	430,542
Investment Grade | Moody's: Aa1, Aa2, Aa3 | S&P: AA+, AA, AA- | State and local governments
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	1,180,898	1,206,441
Investment Grade | Moody's: A1, A2, A3 | S&P: A+, A, A- | State and local governments
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	37,337	37,162
Investment Grade | Moody's: Not Rated | S&P: Not Rated | State and local governments
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	$ 9,961	$ 8,495