Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 2,752,364	$ 4,320,884
Available-for-Sale: Gross Unrealized Gains	1,192	21,460
Available-for-Sale: Gross Unrealized Losses	(328,948)	(66,288)
Available-for-Sale: Fair Value	2,424,608	4,276,056
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	5,461,160	4,694,780
Held-to-Maturity: Gross Unrealized Gains	31	28,334
Held-to-Maturity: Gross Unrealized Losses	(793,117)	(76,495)
Held-to-Maturity: Fair Value	4,668,074	4,646,619
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	259,692	248,858
Available-for-Sale: Gross Unrealized Gains	885	1,513
Available-for-Sale: Gross Unrealized Losses	(16,224)	(284)
Available-for-Sale: Fair Value	244,353	250,087
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	131,587	131,495
Held-to-Maturity: Gross Unrealized Gains		287
Held-to-Maturity: Gross Unrealized Losses	(19,180)	(643)
Held-to-Maturity: Fair Value	112,407	131,139
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	74,057	74,743
Available-for-Sale: Gross Unrealized Gains		1,080
Available-for-Sale: Gross Unrealized Losses	(12,995)	(5)
Available-for-Sale: Fair Value	61,062	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	(140)	(11)
Available-for-Sale: Fair Value	1,618	1,780
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	430,809	384,590
Available-for-Sale: Gross Unrealized Gains		2,339
Available-for-Sale: Gross Unrealized Losses	(60,091)	(3,816)
Available-for-Sale: Fair Value	370,718	383,113
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	17,845	20,316
Held-to-Maturity: Gross Unrealized Gains		76
Held-to-Maturity: Gross Unrealized Losses	(2,522)	(249)
Held-to-Maturity: Fair Value	15,323	20,143
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	864,919	1,327,990
Available-for-Sale: Gross Unrealized Gains	305	9,818
Available-for-Sale: Gross Unrealized Losses	(89,537)	(18,766)
Available-for-Sale: Fair Value	775,687	1,319,042
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	1,900,988	1,774,394
Held-to-Maturity: Gross Unrealized Gains	19	12,139
Held-to-Maturity: Gross Unrealized Losses	(276,868)	(30,621)
Held-to-Maturity: Fair Value	1,624,139	1,755,912
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	949,497	2,127,781
Available-for-Sale: Gross Unrealized Gains	2	4,792
Available-for-Sale: Gross Unrealized Losses	(129,814)	(42,247)
Available-for-Sale: Fair Value	819,685	2,090,326
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	2,958,051	2,286,880
Held-to-Maturity: Gross Unrealized Gains	12	15,508
Held-to-Maturity: Gross Unrealized Losses	(411,442)	(32,627)
Held-to-Maturity: Fair Value	2,546,621	2,269,761
Commercial - Government Agencies or Sponsored Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	171,632	155,164
Available-for-Sale: Gross Unrealized Gains		1,885
Available-for-Sale: Gross Unrealized Losses	(20,147)	(1,159)
Available-for-Sale: Fair Value	151,485	155,890
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	452,689	481,695
Held-to-Maturity: Gross Unrealized Gains		324
Held-to-Maturity: Gross Unrealized Losses	(83,105)	(12,355)
Held-to-Maturity: Fair Value	369,584	469,664
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,986,048	3,610,935
Available-for-Sale: Gross Unrealized Gains	307	16,495
Available-for-Sale: Gross Unrealized Losses	(239,498)	(62,172)
Available-for-Sale: Fair Value	1,746,857	3,565,258
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	5,311,728	4,542,969
Held-to-Maturity: Gross Unrealized Gains	31	27,971
Held-to-Maturity: Gross Unrealized Losses	(771,415)	(75,603)
Held-to-Maturity: Fair Value	$ 4,540,344	$ 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, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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