Investment Securities - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, transfer to held-to-maturity	$ 500,800,000
Unrealized gains on securities transferred from AFS to HTM		$ 1,000,000
Available-for-sale, transfer to held-to-maturity, gain (loss)	$ 0
Amortized Cost		1,530,500,000	$ 335,946,000
Available-for-sale, amortized cost		7,130,861,000	3,397,043,000
Held-to-maturity, interest receivable		9,700,000
Available-for-sale, interest receivable		23,400,000
Available-for-sale securities		7,113,545,000	3,473,598,000
Securities valued at less than historical cost, amount		$ 5,065,704,000
Securities continuous unrealized loss position fair value (as percent)		71.20%
Decrease in available-for-sale provision for credit losses		$ (312,000)	(61,000)	$ 0
Securities pledged as collateral		3,900,000,000	2,000,000,000
Realized gains		15,900,000	54,800,000	13,300,000
Realized losses		$ 422,000	$ 15,000	$ 4,000
Income tax benefit related to security gains (losses) (as percent)		26.135%	26.135%	26.135%
Bonds
Debt Securities, Available-for-sale [Line Items]
Investments sold, amount		$ 342,600,000	$ 1,700,000,000
Commercial Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		4,900,000	7,700,000
Available-for-sale, amortized cost		1,530,000,000	406,100,000
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		65,500,000	14,700,000
Available-for-sale, amortized cost		$ 2,920,000,000	$ 988,800,000