Debt Securities - Debt Securities in an Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2025 USD ($) security	Dec. 31, 2024 USD ($) security
Available-for-sale
Number of Securities | security	642	662
Less than 12 Months, Fair Value	$ 58,370	$ 57,410
Less than 12 Months, Unrealized Loss	(1,058)	(1,351)
12 Months or More, Fair Value	4,063,334	4,165,269
12 Months or More, Unrealized Loss	(349,656)	(409,981)
Total, Fair Value	4,121,704	4,222,679
Total, Unrealized Loss	$ (350,714)	$ (411,332)
U.S. government and federal agency
Available-for-sale
Number of Securities | security	48	55
Less than 12 Months, Fair Value	$ 3,320	$ 3,756
Less than 12 Months, Unrealized Loss	(36)	(34)
12 Months or More, Fair Value	466,542	463,151
12 Months or More, Unrealized Loss	(11,835)	(15,620)
Total, Fair Value	469,862	466,907
Total, Unrealized Loss	$ (11,871)	$ (15,654)
U.S. government sponsored enterprises
Available-for-sale
Number of Securities | security	14	14
Less than 12 Months, Fair Value	$ 0	$ 0
Less than 12 Months, Unrealized Loss	0	0
12 Months or More, Fair Value	313,508	310,154
12 Months or More, Unrealized Loss	(10,815)	(13,700)
Total, Fair Value	313,508	310,154
Total, Unrealized Loss	$ (10,815)	$ (13,700)
State and local governments
Available-for-sale
Number of Securities | security	47	50
Less than 12 Months, Fair Value	$ 3,678	$ 3,653
Less than 12 Months, Unrealized Loss	(74)	(35)
12 Months or More, Fair Value	48,283	49,748
12 Months or More, Unrealized Loss	(3,037)	(3,237)
Total, Fair Value	51,961	53,401
Total, Unrealized Loss	$ (3,111)	$ (3,272)
Corporate bonds
Available-for-sale
Number of Securities | security	2	2
Less than 12 Months, Fair Value	$ 0	$ 0
Less than 12 Months, Unrealized Loss	0	0
12 Months or More, Fair Value	13,872	13,707
12 Months or More, Unrealized Loss	(145)	(315)
Total, Fair Value	13,872	13,707
Total, Unrealized Loss	$ (145)	$ (315)
Residential mortgage-backed securities
Available-for-sale
Number of Securities | security	381	389
Less than 12 Months, Fair Value	$ 9,183	$ 13,535
Less than 12 Months, Unrealized Loss	(66)	(240)
12 Months or More, Fair Value	2,262,963	2,341,700
12 Months or More, Unrealized Loss	(262,951)	(304,579)
Total, Fair Value	2,272,146	2,355,235
Total, Unrealized Loss	$ (263,017)	$ (304,819)
Commercial mortgage-backed securities
Available-for-sale
Number of Securities | security	150	152
Less than 12 Months, Fair Value	$ 42,189	$ 36,466
Less than 12 Months, Unrealized Loss	(882)	(1,042)
12 Months or More, Fair Value	958,166	986,809
12 Months or More, Unrealized Loss	(60,873)	(72,530)
Total, Fair Value	1,000,355	1,023,275
Total, Unrealized Loss	$ (61,755)	$ (73,572)