Investment Securities - Amortized Cost and Approximate Fair Value of Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Available for sale securities
Amortized Cost	$ 2,542,432	$ 2,268,655
Gross Unrealized Gains	3,064	89,536
Gross Unrealized Losses	249,145	13,640
Fair Value	2,296,351	2,344,551
Held to maturity securities
Amortized Cost	2,333,924	2,180,047
Allowance for Credit Losses	245	245
Net Carrying Amount	2,333,679	2,179,802
Gross Unrealized Gains	1,411	37,776
Gross Unrealized Losses	309,811	15,320
Fair Value	2,025,524	2,202,503
U.S. Treasury
Available for sale securities
Amortized Cost	16,300	1,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	111	1
Fair Value	16,189	999
U.S. Government-sponsored agency securities
Available for sale securities
Amortized Cost	134,594	96,244
Gross Unrealized Gains	204	437
Gross Unrealized Losses	10,186	1,545
Fair Value	124,612	95,136
Held to maturity securities
Amortized Cost	393,331	371,457
Allowance for Credit Losses	0	0
Net Carrying Amount	393,331	371,457
Gross Unrealized Gains	0	226
Gross Unrealized Losses	47,376	7,268
Fair Value	345,955	364,415
State and municipal
Available for sale securities
Amortized Cost	1,665,253	1,495,696
Gross Unrealized Gains	2,687	81,734
Gross Unrealized Losses	162,690	898
Fair Value	1,505,250	1,576,532
Held to maturity securities
Amortized Cost	1,117,526	1,057,301
Allowance for Credit Losses	245	245
Net Carrying Amount	1,117,281	1,057,056
Gross Unrealized Gains	1,368	29,593
Gross Unrealized Losses	183,539	2,170
Fair Value	935,355	1,084,724
U.S. Government-sponsored mortgage-backed securities
Available for sale securities
Amortized Cost	712,216	671,684
Gross Unrealized Gains	168	7,109
Gross Unrealized Losses	75,925	11,188
Fair Value	636,459	667,605
Held to maturity securities
Amortized Cost	821,567	749,789
Allowance for Credit Losses	0	0
Net Carrying Amount	821,567	749,789
Gross Unrealized Gains	43	7,957
Gross Unrealized Losses	78,881	5,881
Fair Value	742,729	751,865
Corporate obligations
Available for sale securities
Amortized Cost	14,069	4,031
Gross Unrealized Gains	5	256
Gross Unrealized Losses	233	8
Fair Value	13,841	4,279
Foreign investment
Held to maturity securities
Amortized Cost	1,500	1,500
Allowance for Credit Losses	0	0
Net Carrying Amount	1,500	1,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	15	1
Fair Value	$ 1,485	$ 1,499

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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Amount, before tax, of unrealized loss 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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