Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 4,412,330	$ 4,320,884
Available-for-Sale: Gross Unrealized Gains	2,221	21,460
Available-for-Sale: Gross Unrealized Losses	(459,075)	(66,288)
Available-for-Sale: Fair Value	3,955,476	4,276,056
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	4,321,693	4,694,780
Held-to-Maturity: Gross Unrealized Gains	742	28,334
Held-to-Maturity: Gross Unrealized Losses	(498,696)	(76,495)
Held-to-Maturity: Fair Value	3,823,739	4,646,619
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	272,935	248,858
Available-for-Sale: Gross Unrealized Gains	1,640	1,513
Available-for-Sale: Gross Unrealized Losses	(10,689)	(284)
Available-for-Sale: Fair Value	263,886	250,087
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	131,556	131,495
Held-to-Maturity: Gross Unrealized Gains		287
Held-to-Maturity: Gross Unrealized Losses	(13,058)	(643)
Held-to-Maturity: Fair Value	118,498	131,139
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	74,698	74,743
Available-for-Sale: Gross Unrealized Gains	2	1,080
Available-for-Sale: Gross Unrealized Losses	(8,859)	(5)
Available-for-Sale: Fair Value	65,841	75,818
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,758	1,758
Available-for-Sale: Gross Unrealized Gains		33
Available-for-Sale: Gross Unrealized Losses	(85)	(11)
Available-for-Sale: Fair Value	1,673	1,780
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	432,016	384,590
Available-for-Sale: Gross Unrealized Gains		2,339
Available-for-Sale: Gross Unrealized Losses	(47,697)	(3,816)
Available-for-Sale: Fair Value	384,319	383,113
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	18,672	20,316
Held-to-Maturity: Gross Unrealized Gains		76
Held-to-Maturity: Gross Unrealized Losses	(1,857)	(249)
Held-to-Maturity: Fair Value	16,815	20,143
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,348,519	1,327,990
Available-for-Sale: Gross Unrealized Gains	566	9,818
Available-for-Sale: Gross Unrealized Losses	(122,746)	(18,766)
Available-for-Sale: Fair Value	1,226,339	1,319,042
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	1,605,791	1,774,394
Held-to-Maturity: Gross Unrealized Gains	721	12,139
Held-to-Maturity: Gross Unrealized Losses	(173,760)	(30,621)
Held-to-Maturity: Fair Value	1,432,752	1,755,912
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	2,104,396	2,127,781
Available-for-Sale: Gross Unrealized Gains	13	4,792
Available-for-Sale: Gross Unrealized Losses	(254,542)	(42,247)
Available-for-Sale: Fair Value	1,849,867	2,090,326
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	2,107,997	2,286,880
Held-to-Maturity: Gross Unrealized Gains	21	15,508
Held-to-Maturity: Gross Unrealized Losses	(247,438)	(32,627)
Held-to-Maturity: Fair Value	1,860,580	2,269,761
Commercial - Government Agencies or Sponsored Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	178,008	155,164
Available-for-Sale: Gross Unrealized Gains		1,885
Available-for-Sale: Gross Unrealized Losses	(14,457)	(1,159)
Available-for-Sale: Fair Value	163,551	155,890
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	457,677	481,695
Held-to-Maturity: Gross Unrealized Gains		324
Held-to-Maturity: Gross Unrealized Losses	(62,583)	(12,355)
Held-to-Maturity: Fair Value	395,094	469,664
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	3,630,923	3,610,935
Available-for-Sale: Gross Unrealized Gains	579	16,495
Available-for-Sale: Gross Unrealized Losses	(391,745)	(62,172)
Available-for-Sale: Fair Value	3,239,757	3,565,258
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	4,171,465	4,542,969
Held-to-Maturity: Gross Unrealized Gains	742	27,971
Held-to-Maturity: Gross Unrealized Losses	(483,781)	(75,603)
Held-to-Maturity: Fair Value	$ 3,688,426	$ 4,495,337

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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Amount of 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 allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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