Investment Securities - Narrative (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2022 USD ($) investment_security	Mar. 31, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) investment_security	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) investment_security
Investment Securities
Net carrying amount of securities transferred from available-for-sale to held-to-maturity				$ 1,019,472,000	$ 0
Accumulated other comprehensive loss, net of tax	$ (215,018,000)			(215,018,000)		$ (7,862,000)
Investments held-to-maturity, allowance for credit losses	109,000	$ 41,000		109,000		22,000
Investments held-to-maturity, provision for credit losses	68,000	19,000	$ 0	87,000	0
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	$ 19,500,000			$ 19,500,000		$ 17,300,000
FRB stock	74,500,000			74,500,000		74,500,000
Other stock	24,600,000			24,600,000		25,700,000
Impairment loss on investments in FHLB, FRB and other stock				0
Public deposits, Other Borrowings, and Other Purposes | Asset Pledged as Collateral
Investment Securities
Investments at carrying value	87,300,000			87,300,000		130,700,000
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Investment Securities
Accumulated other comprehensive loss before tax amount	(229,400,000)			(229,400,000)		(4,700,000)
Accumulated other comprehensive loss, net of tax	(163,900,000)			(163,900,000)		$ (3,300,000)
Municipal bonds
Investment Securities
Securities transferred from available-for-sale to held-to-maturity	444,600,000
Net carrying amount of securities transferred from available-for-sale to held-to-maturity	400,800,000
Debt securities, held-to-maturity, transfer, unrealized loss	43,800,000
Accumulated other comprehensive loss before tax amount	(71,500,000)			(71,500,000)
Accumulated other comprehensive loss, net of tax	$ (51,100,000)			$ (51,100,000)