Investment Securities - Amortized Cost and Approximate Fair Values of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Available for sale securities
Amortized Cost	$ 2,268,655	$ 1,807,389
Gross Unrealized Gains	89,536	112,079
Gross Unrealized Losses	13,640	349
Fair Value	2,344,551	1,919,119
Held to maturity securities
Amortized Cost	2,180,047	1,227,668
Allowance for Credit Losses	245	0
Net Carrying Amount	2,179,802	1,227,668
Gross Unrealized Gains	37,776	52,877
Gross Unrealized Losses	15,320	252
Fair Value	2,202,503	1,280,293
U.S. Treasury
Available for sale securities
Amortized Cost	1,000
Gross Unrealized Gains	0
Gross Unrealized Losses	1
Fair Value	999
U.S. Government-sponsored agency securities
Available for sale securities
Amortized Cost	96,244	43,437
Gross Unrealized Gains	437	1,571
Gross Unrealized Losses	1,545	0
Fair Value	95,136	45,008
Held to maturity securities
Amortized Cost	371,457	145,398
Allowance for Credit Losses	0	0
Net Carrying Amount	371,457	145,398
Gross Unrealized Gains	226	347
Gross Unrealized Losses	7,268	220
Fair Value	364,415	145,525
State and municipal
Available for sale securities
Amortized Cost	1,495,696	1,168,711
Gross Unrealized Gains	81,734	89,420
Gross Unrealized Losses	898	246
Fair Value	1,576,532	1,257,885
Held to maturity securities
Amortized Cost	1,057,301	619,927
Allowance for Credit Losses	245	0
Net Carrying Amount	1,057,056	619,927
Gross Unrealized Gains	29,593	34,978
Gross Unrealized Losses	2,170	32
Fair Value	1,084,724	654,873
U.S. Government-sponsored mortgage-backed securities
Available for sale securities
Amortized Cost	671,684	591,210
Gross Unrealized Gains	7,109	20,984
Gross Unrealized Losses	11,188	103
Fair Value	667,605	612,091
Held to maturity securities
Amortized Cost	749,789	460,843
Allowance for Credit Losses	0	0
Net Carrying Amount	749,789	460,843
Gross Unrealized Gains	7,957	17,552
Gross Unrealized Losses	5,881	0
Fair Value	751,865	478,395
Corporate obligations
Available for sale securities
Amortized Cost	4,031	4,031
Gross Unrealized Gains	256	104
Gross Unrealized Losses	8	0
Fair Value	4,279	4,135
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	1	0
Fair Value	$ 1,499	$ 1,500

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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