Investment Securities - Amortized Cost and Approximate Fair Values of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Available for sale securities
Amortized Cost	$ 2,273,347	$ 2,268,655
Gross Unrealized Gains	439	89,536
Gross Unrealized Losses	297,125	13,640
Fair Value	1,976,661	2,344,551
Held to maturity securities
Amortized Cost	2,287,372	2,180,047
Allowance for Credit Losses	245	245
Net Carrying Amount	2,287,127	2,179,802
Gross Unrealized Gains	647	37,776
Gross Unrealized Losses	380,154	15,320
Fair Value	1,907,865	2,202,503
U.S. Treasury
Available for sale securities
Amortized Cost	2,501	1,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	42	1
Fair Value	2,459	999
U.S. Government-sponsored agency securities
Available for sale securities
Amortized Cost	119,154	96,244
Gross Unrealized Gains	0	437
Gross Unrealized Losses	17,192	1,545
Fair Value	101,962	95,136
Held to maturity securities
Amortized Cost	392,246	371,457
Allowance for Credit Losses	0	0
Net Carrying Amount	392,246	371,457
Gross Unrealized Gains	0	226
Gross Unrealized Losses	69,147	7,268
Fair Value	323,099	364,415
State and municipal
Available for sale securities
Amortized Cost	1,530,048	1,495,696
Gross Unrealized Gains	438	81,734
Gross Unrealized Losses	178,726	898
Fair Value	1,351,760	1,576,532
Held to maturity securities
Amortized Cost	1,117,552	1,057,301
Allowance for Credit Losses	245	245
Net Carrying Amount	1,117,307	1,057,056
Gross Unrealized Gains	647	29,593
Gross Unrealized Losses	197,064	2,170
Fair Value	921,135	1,084,724
U.S. Government-sponsored mortgage-backed securities
Available for sale securities
Amortized Cost	608,630	671,684
Gross Unrealized Gains	1	7,109
Gross Unrealized Losses	100,358	11,188
Fair Value	508,273	667,605
Held to maturity securities
Amortized Cost	776,074	749,789
Allowance for Credit Losses	0	0
Net Carrying Amount	776,074	749,789
Gross Unrealized Gains	0	7,957
Gross Unrealized Losses	113,915	5,881
Fair Value	662,159	751,865
Corporate obligations
Available for sale securities
Amortized Cost	13,014	4,031
Gross Unrealized Gains	0	256
Gross Unrealized Losses	807	8
Fair Value	12,207	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	28	1
Fair Value	$ 1,472	$ 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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