Investment Securities - Narrative (Details)	3 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($)	Dec. 31, 2021 USD ($) investment_security	Dec. 31, 2020 USD ($) investment_security	Dec. 31, 2019 USD ($)	Jul. 01, 2021 USD ($)
Investment Holdings [Line Items]
Transfers of investment securities from available-for-sale to held-to-maturity		$ 319,924,000	$ 0	$ 0
Unrealized loss on securities transferred from available-for-sale to held-to-maturity		1,649,000	0
Accumulated other comprehensive income (loss), net of tax		(7,862,000)	60,292,000
Available-for-sale securities acquired		2,231,699,000	2,715,499,000	889,516,000
Investments held-to-maturity, allowance for credit losses		22,000	0
Provision for Credit Losses		22,000	0
Allowance for credit losses on debt securities, available-for-sale		0	0
Available-for-sale securities, provision for credit losses		$ 0	$ 0
OTTI on investment securities				0
Available-for-sale and held-to-maturity securities in nonaccrual status | investment_security		0	0
Available-for-sale and held-to-maturity securities purchased with deterioration in credit quality | investment_security		0	0
Available-for-sale and held-to-maturity collateral dependent | investment_security		0	0
Gross gains		$ 23,200,000	$ 15,700,000	10,300,000
Gross losses		6,300,000	1,800,000	1,800,000
Proceeds from available-for-sale securities		901,100,000	766,500,000	551,800,000
Investment securities pledged		130,700,000	147,300,000
FHLB stock		17,300,000
FRB stock		74,500,000
Other stock		25,700,000
FHLB repurchases		0	17,300,000	$ 18,300,000
Impairment loss on investments in FHLB, FRB and other stock		0
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Investment Holdings [Line Items]
Accumulated other comprehensive income (loss) before tax		(4,700,000)	84,400,000
Accumulated other comprehensive income (loss), net of tax		(3,300,000)	60,300,000
Opus
Investment Holdings [Line Items]
Available-for-sale securities acquired	$ 829,900,000
Allowance for credit losses of available-for-sale securities classified as purchase credit deteriorated	0
Opus | Financial Asset Acquired with Credit Deterioration
Investment Holdings [Line Items]
Available-for-sale securities acquired	$ 0
Mortgage-backed securities
Investment Holdings [Line Items]
Unrealized loss on securities transferred from available-for-sale to held-to-maturity		0	$ 0
Municipal bonds
Investment Holdings [Line Items]
Securities transferred from available-for-sale to held-to-maturity		326,500,000
Transfers of investment securities from available-for-sale to held-to-maturity		319,900,000
Unrealized loss on securities transferred from available-for-sale to held-to-maturity		1,649,000			$ 6,600,000
Accumulated other comprehensive income (loss) before tax		(6,300,000)
Accumulated other comprehensive income (loss), net of tax		$ (4,500,000)