Investment Securities - Textual (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	$ 932,484,000		$ 932,484,000		$ 335,946,000
Available for sale mortgage backed securities	6,543,022,000		6,543,022,000		3,397,043,000
Held-to-maturity, interest receivable	4,200,000		4,200,000
Available-for-sale, interest receivable	21,800,000		21,800,000
Available-for-sale securities	6,556,581,000		6,556,581,000		3,473,598,000
Securities valued at less than historical cost, amount	$ 3,183,965,000		$ 3,183,965,000
Securities valued at less than historical cost (as percent)	48.60%		48.60%
Decrease in available-for-sale provision for credit losses	$ (2,454,000)	$ 340,000	$ (312,000)	$ 236,000
Securities pledged as collateral	3,890,000,000		3,890,000,000		2,010,000,000.00
Realized gains	5,200,000	391,000	10,600,000	32,500,000
Realized losses	26,000	(1,000)	39,000	$ (2,600)
Investments sold, amount		$ 1,200,000,000	$ 249,500,000
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	6,100,000		$ 6,100,000		7,700,000
Available for sale mortgage backed securities	1,340,000,000		1,340,000,000		406,100,000
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	54,500,000		54,500,000		14,700,000
Available for sale mortgage backed securities	$ 2,650,000,000		$ 2,650,000,000		$ 988,800,000