Investment Securities - Narrative (Details)	3 Months Ended				9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($) 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					$ 112,700,000
Available-for-sale, transfer to held-to-maturity, gain (loss)					0
Held to maturity mortgage backed securities	$ 3,661,914,000				3,661,914,000		$ 3,729,502,000
Available for sale mortgage backed securities	2,976,811,000				2,976,811,000		3,509,709,000
Held-to-maturity, interest receivable	17,300,000				17,300,000
Available-for-sale, interest receivable	24,600,000				24,600,000
Available-for-sale securities	2,691,094,000				2,691,094,000		3,152,153,000
Securities valued at less than historical cost, amount	$ 2,613,507,000				$ 2,613,507,000
Securities valued at less than historical cost (as percent)	97.10%				97.10%
Provision for credit losses, AFS securities	$ 0				$ 0
Net decrease in allowance on previously impaired securities		$ 1,200,000				$ 2,526,000
Securities charged-off						7,000,000
Securities pledged as collateral	2,490,000,000				2,490,000,000		3,320,000,000
Realized gains	0	0			0	0
Realized losses	28,400,000	0			$ 28,400,000	$ 391,000
Investments sold, amount	251,500,000
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	137,200,000				$ 137,200,000		141,600,000
Available for sale mortgage backed securities	571,900,000				571,900,000		710,100,000
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	955,900,000				955,900,000		1,020,000,000.00
Available for sale mortgage backed securities	938,500,000				938,500,000		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	256,155,000				256,155,000		256,007,000
Available for sale mortgage backed securities	239,053,000				239,053,000		259,165,000
Available-for-sale securities	222,827,000				222,827,000		$ 234,297,000
Securities valued at less than historical cost, amount	$ 175,596,000				$ 175,596,000
Net decrease in allowance on previously impaired securities		$ 1,200,000				$ 2,526,000
Securities charged-off						$ 7,000,000