Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Available-for-Sale Debt Securities
Amortized Cost	$ 5,249,882,000	$ 2,450,265,000
Gross Unrealized Gain	34,626,000	80,871,000
Gross Unrealized Loss	79,197,000	2,079,000
Allowance for Credit Losses	0	0
Fair Value	5,205,311,000	2,529,057,000
Held-to-Maturity Debt Securities
Investment securities, held to maturity, net	90,646,000	111,747,000
Gross Unrealized Gain	3,489,000	4,680,000
Gross Unrealized Loss	0	0
Allowance for Credit Losses	4,000	6,000
Fair Value	94,131,000	116,421,000
State and political subdivisions
Held-to-Maturity Debt Securities
Investment securities, held to maturity, net	90,146,000	111,246,000
Gross Unrealized Gain	3,489,000	4,678,000
Gross Unrealized Loss	0	0
Allowance for Credit Losses	4,000	6,000	$ 0
Fair Value	93,631,000	115,918,000
Available for sale securities transfers to held to maturity unrealized gains	200,000	400,000
Foreign bonds
Held-to-Maturity Debt Securities
Investment securities, held to maturity, net	500,000	501,000
Gross Unrealized Gain	0	2,000
Gross Unrealized Loss	0	0
Allowance for Credit Losses	0	0
Fair Value	500,000	503,000
Collateralized mortgage obligation (CMO)
Available-for-Sale Debt Securities
Amortized Cost	586,830,000	461,819,000
Gross Unrealized Gain	3,569,000	9,949,000
Gross Unrealized Loss	14,633,000	443,000
Allowance for Credit Losses	0	0
Fair Value	575,766,000	471,325,000
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Available-for-Sale Debt Securities
Amortized Cost	4,275,307,000	1,544,105,000
Gross Unrealized Gain	24,170,000	55,747,000
Gross Unrealized Loss	53,793,000	882,000
Allowance for Credit Losses	0	0
Fair Value	4,245,684,000	1,598,970,000
Freddie Mac (FHLMC) MBS
Available-for-Sale Debt Securities
Amortized Cost	139,708,000	190,856,000
Gross Unrealized Gain	6,336,000	12,142,000
Gross Unrealized Loss	516,000	105,000
Allowance for Credit Losses	0	0
Fair Value	145,528,000	202,893,000
Ginnie Mae (GNMA) MBS
Available-for-Sale Debt Securities
Amortized Cost	17,456,000	22,716,000
Gross Unrealized Gain	551,000	1,046,000
Gross Unrealized Loss	71,000	0
Allowance for Credit Losses	0	0
Fair Value	17,936,000	23,762,000
Government-sponsored enterprises (GSE) agency notes
Available-for-Sale Debt Securities
Amortized Cost	230,581,000	230,769,000
Gross Unrealized Gain	0	1,987,000
Gross Unrealized Loss	10,184,000	649,000
Allowance for Credit Losses	0	0
Fair Value	$ 220,397,000	$ 232,107,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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