Investment Securities - Narrative (Details)	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2022 USD ($) investment_security	Jun. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Sep. 30, 2022 USD ($) investment_security	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) investment_security	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Investment Securities
Securities transferred from available-for-sale to held-to-maturity	$ 0
Net carrying amount of securities transferred from available-for-sale to held-to-maturity					$ 1,019,472,000	$ 154,456,000
Accumulated other comprehensive loss, net of tax	(281,113,000)				(281,113,000)		$ (7,862,000)
Investments held-to-maturity, allowance for credit losses	91,000	$ 109,000	$ 11,000	$ 109,000	91,000	11,000	22,000	$ 0	$ 0
Investments held-to-maturity, provision (recapture) for credit losses	(18,000)		11,000		69,000	11,000
Allowance for credit losses on debt securities, Available-for-sale	0				0		$ 0
Available-for-sale securities, provision for credit losses	$ 0	$ 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
FHLB stock	$ 19,400,000				$ 19,400,000		$ 17,300,000
FRB stock	74,700,000				74,700,000		74,500,000
Other stock	24,700,000				24,700,000		25,700,000
Impairment loss on investments in FHLB, FRB and other stock					0
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Investment Securities
Accumulated other comprehensive loss before tax amount	(324,300,000)				(324,300,000)		(4,700,000)
Accumulated other comprehensive loss, net of tax	(231,700,000)				(231,700,000)		(3,300,000)
Public deposits, Other Borrowings, and Other Purposes | Asset Pledged as Collateral
Investment Securities
Investments at carrying value	194,000,000				194,000,000		$ 130,700,000
Municipal bonds
Investment Securities
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)
Accumulated other comprehensive loss before tax amount	(69,200,000)				(69,200,000)
Accumulated other comprehensive loss, net of tax	$ (49,400,000)				$ (49,400,000)
Mortgage-backed securities
Investment Securities
Securities transferred from available-for-sale to held-to-maturity				255,000,000
Net carrying amount of securities transferred from available-for-sale to held-to-maturity				238,800,000
Debt securities, held-to-maturity, transfer, unrealized loss				$ (16,200,000)