Investment Securities - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) investment_security	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) investment_security	Jun. 30, 2022 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) investment_security	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Summary of Investment Holdings [Line Items]
Net carrying amount of securities transferred from available-for-sale to held-to-maturity			$ 360,347,000	$ 1,019,472,000
Accumulated other comprehensive loss, net of tax	$ (275,467,000)		(275,467,000)			$ (265,247,000)
Investments held-to-maturity, allowance for credit losses	113,000	$ 109,000	113,000	109,000	$ 227,000	43,000	$ 41,000	$ 22,000
Allowance for credit losses	0		0			$ 0
Available-for-sale securities, provision for credit losses	$ 0	$ 0	$ 0	0
Available-for-sale and held-to-maturity securities in nonaccrual status | investment_security	0		0			0
Available-for-sale and held-to-maturity securities purchased with deterioration in credit quality | investment_security	0		0			0
Available-for-sale and held-to-maturity collateral dependent | investment_security	0		0			0
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Summary of Investment Holdings [Line Items]
Accumulated other comprehensive loss before tax amount	$ (274,700,000)		$ (274,700,000)			$ (303,700,000)
Accumulated other comprehensive loss, net of tax	(196,600,000)		(196,600,000)			(217,400,000)
AOCI, Accumulated Gain (Loss), Debt Securities Transferred To Held-To-Maturity, Available-For-Sale, Parent
Summary of Investment Holdings [Line Items]
Accumulated other comprehensive loss before tax amount	(110,100,000)		(110,100,000)
Accumulated other comprehensive loss, net of tax	(78,800,000)		(78,800,000)
Public deposits, Other Borrowings, and Other Purposes | Asset Pledged as Collateral
Summary of Investment Holdings [Line Items]
Investments at carrying value	3,700,000,000		3,700,000,000			195,600,000
Federal Reserve Discount Window | Asset Pledged as Collateral
Summary of Investment Holdings [Line Items]
Investments at carrying value	1,680,000,000		1,680,000,000
Federal Reserves New Bank Term Funding Program | Asset Pledged as Collateral
Summary of Investment Holdings [Line Items]
Investments at carrying value	1,830,000,000		1,830,000,000
Mortgage-backed securities
Summary of Investment Holdings [Line Items]
Securities transferred from available-for-sale to held-to-maturity			410,700,000	255,000,000
Net carrying amount of securities transferred from available-for-sale to held-to-maturity			360,300,000	238,800,000
Debt securities, held-to-maturity, transfer, unrealized loss			(50,400,000)	(16,200,000)
Investments held-to-maturity, allowance for credit losses	0		0			0
Municipal bonds
Summary of Investment Holdings [Line Items]
Securities transferred from available-for-sale to held-to-maturity				831,400,000
Net carrying amount of securities transferred from available-for-sale to held-to-maturity				780,700,000
Debt securities, held-to-maturity, transfer, unrealized loss				$ (50,800,000)
Investments held-to-maturity, allowance for credit losses	$ 113,000		$ 113,000			$ 43,000
U.S. Treasury, U.S. Government Agency, and U.S. Government-Sponsored Enterprise Securities
Summary of Investment Holdings [Line Items]
Percentage of total debt securities, available for sale	75.00%		75.00%