Investment Securities - Textual (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
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, unrealized gain (loss)	$ (148,300,000)		738,000
Available-for-sale, transfer to held-to-maturity, gain (loss)				$ 0
Held to maturity mortgage backed securities	3,788,460,000			3,788,460,000		$ 1,530,500,000
Available for sale mortgage backed securities	4,484,131,000			4,484,131,000		7,130,861,000
Held-to-maturity, interest receivable	17,700,000			17,700,000
Available-for-sale, interest receivable	16,200,000			16,200,000
Available-for-sale securities	3,937,543,000			3,937,543,000		7,113,545,000
Securities valued at less than historical cost, amount	$ 3,878,698,000			$ 3,878,698,000
Securities valued at less than historical cost (as percent)	98.50%			98.50%
Securities - AFS	$ 0		0	$ 0	$ (312,000)
Provision for credit losses					(312,000)
Allowance for credit losses on HTM	1,384,000	1,381,000	1,279,000	1,384,000	1,279,000	1,279,000	$ 1,132,000	$ 2,915,000
Securities pledged as collateral	3,930,000,000			3,930,000,000		3,880,000,000
Realized gains	8,000		5,300,000	45,000	15,900,000
Realized losses	(30,000)		(24,500)	$ (271,000)	$ (63,600)
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	150,000,000			$ 150,000,000		4,900,000
Available for sale mortgage backed securities	1,170,000,000			1,170,000,000		1,530,000,000
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	1,060,000,000.00			1,060,000,000.00		65,500,000
Available for sale mortgage backed securities	1,500,000,000			1,500,000,000		2,920,000,000
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	1,865,310,000			1,865,310,000		1,210,248,000
Available for sale mortgage backed securities	1,054,356,000			1,054,356,000		1,791,097,000
Available-for-sale securities	822,509,000			822,509,000		1,819,658,000
Securities valued at less than historical cost, amount	795,657,000			795,657,000
Allowance for credit losses on HTM	107,000	$ 103,000	$ 1,196,000	107,000	$ 1,196,000	$ 1,197,000	$ 871,000	$ 2,307,000
State and political subdivisions | Other Credit Enhancement or Insurance
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	953,072,000			953,072,000
Allowance for credit losses on HTM	$ 0			$ 0