Debt Securities - Debt Securities in an Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Available-for-sale
Number of available-for-sale securities | security	757	794
Less than 12 months, fair value	$ 79,718	$ 1,075,458
Less than 12 months, unrealized loss	(3,962)	(69,730)
12 months or more, fair value	4,624,256	4,144,180
12 months or more, unrealized loss	(665,027)	(554,151)
Total, fair value	4,703,974	5,219,638
Total, unrealized loss	$ (668,989)	$ (623,881)
U.S. government and federal agency
Available-for-sale
Number of available-for-sale securities | security	57	56
Less than 12 months, fair value	$ 2,724	$ 4,150
Less than 12 months, unrealized loss	(40)	(64)
12 months or more, fair value	437,769	435,375
12 months or more, unrealized loss	(41,324)	(42,552)
Total, fair value	440,493	439,525
Total, unrealized loss	$ (41,364)	$ (42,616)
U.S. government sponsored enterprises
Available-for-sale
Number of available-for-sale 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	289,831	287,364
12 months or more, unrealized loss	(31,701)	(32,793)
Total, fair value	289,831	287,364
Total, unrealized loss	$ (31,701)	$ (32,793)
State and local governments
Available-for-sale
Number of available-for-sale securities | security	108	121
Less than 12 months, fair value	$ 17,903	$ 71,512
Less than 12 months, unrealized loss	(438)	(2,109)
12 months or more, fair value	62,015	20,753
12 months or more, unrealized loss	(5,647)	(2,640)
Total, fair value	79,918	92,265
Total, unrealized loss	$ (6,085)	$ (4,749)
Corporate bonds
Available-for-sale
Number of available-for-sale securities | security	5	5
Less than 12 months, fair value	$ 0	$ 25,146
Less than 12 months, unrealized loss	0	(992)
12 months or more, fair value	25,028	0
12 months or more, unrealized loss	(1,117)	0
Total, fair value	25,028	25,146
Total, unrealized loss	$ (1,117)	$ (992)
Residential mortgage-backed securities
Available-for-sale
Number of available-for-sale securities | security	414	441
Less than 12 months, fair value	$ 1,598	$ 301,548
Less than 12 months, unrealized loss	(79)	(24,581)
12 months or more, fair value	2,809,172	2,965,512
12 months or more, unrealized loss	(470,315)	(414,511)
Total, fair value	2,810,770	3,267,060
Total, unrealized loss	$ (470,394)	$ (439,092)
Commercial mortgage-backed securities
Available-for-sale
Number of available-for-sale securities | security	159	157
Less than 12 months, fair value	$ 57,493	$ 673,102
Less than 12 months, unrealized loss	(3,405)	(41,984)
12 months or more, fair value	1,000,441	435,176
12 months or more, unrealized loss	(114,923)	(61,655)
Total, fair value	1,057,934	1,108,278
Total, unrealized loss	$ (118,328)	$ (103,639)