Investment Securities - Narrative (Details)	3 Months Ended				6 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($) bond	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, transfer to held-to-maturity			$ 1,990,000,000	$ 500,800,000
Debt securities, held-to-maturity transfer, unrealized loss					$ 117,400,000
Available-for-sale, transfer to held-to-maturity, gain (loss)					0
Held to maturity mortgage backed securities	$ 3,688,664,000				3,688,664,000		$ 3,729,502,000
Available for sale mortgage backed securities	3,255,738,000				3,255,738,000		3,509,709,000
Held-to-maturity, interest receivable	20,500,000				20,500,000
Available-for-sale, interest receivable	26,700,000				26,700,000
Available-for-sale securities	2,885,904,000				2,885,904,000		3,152,153,000
Securities valued at less than historical cost, amount	$ 2,824,349,000				$ 2,824,349,000
Securities valued at less than historical cost (as percent)	97.90%				97.90%
Provision for credit losses, AFS securities	$ 0				$ 0
Net decrease in allowance on previously impaired securities		$ 1,326,000				$ 1,326,000
Securities charged-off						7,000,000
Securities pledged as collateral	2,730,000,000				2,730,000,000		3,320,000,000
Realized gains	0	0			0	0
Realized losses	0	391,000			$ 0	$ 391,000
Income tax benefit related to security gains (losses) (as percent)					26.135%	26.135%
Commercial Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	139,000,000.0				$ 139,000,000.0		141,600,000
Available for sale mortgage backed securities	597,700,000				597,700,000		710,100,000
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	980,700,000				980,700,000		1,020,000,000.00
Available for sale mortgage backed securities	1,130,000,000				1,130,000,000		1,230,000,000
Bonds
Debt Securities, Available-for-sale [Line Items]
Number of uncollectible bonds | bond						1
Other securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	256,835,000				256,835,000		256,007,000
Available for sale mortgage backed securities	244,091,000				244,091,000		259,165,000
Available-for-sale securities	223,034,000				223,034,000		$ 234,297,000
Securities valued at less than historical cost, amount	$ 175,815,000				$ 175,815,000
Net decrease in allowance on previously impaired securities		$ 1,326,000				$ 1,326,000
Securities charged-off						$ 7,000,000