Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 4,548,509	$ 4,320,884
Available-for-Sale: Gross Unrealized Gains	2,559	21,460
Available-for-Sale: Gross Unrealized Losses	(292,534)	(66,288)
Available-for-Sale: Fair Value	4,258,534	4,276,056
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	4,489,615	4,694,780
Held-to-Maturity: Gross Unrealized Gains	3,806	28,334
Held-to-Maturity: Gross Unrealized Losses	(322,159)	(76,495)
Held-to-Maturity: Fair Value	4,171,262	4,646,619
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	281,530	248,858
Available-for-Sale: Gross Unrealized Gains	1,326	1,513
Available-for-Sale: Gross Unrealized Losses	(7,693)	(284)
Available-for-Sale: Fair Value	275,163	250,087
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	131,526	131,495
Held-to-Maturity: Gross Unrealized Gains		287
Held-to-Maturity: Gross Unrealized Losses	(8,584)	(643)
Held-to-Maturity: Fair Value	122,942	131,139
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	74,724	74,743
Available-for-Sale: Gross Unrealized Gains	6	1,080
Available-for-Sale: Gross Unrealized Losses	(5,062)	(5)
Available-for-Sale: Fair Value	69,668	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	(57)	(11)
Available-for-Sale: Fair Value	1,701	1,780
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	433,216	384,590
Available-for-Sale: Gross Unrealized Gains	12	2,339
Available-for-Sale: Gross Unrealized Losses	(23,622)	(3,816)
Available-for-Sale: Fair Value	409,606	383,113
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	19,496	20,316
Held-to-Maturity: Gross Unrealized Gains		76
Held-to-Maturity: Gross Unrealized Losses	(1,175)	(249)
Held-to-Maturity: Fair Value	18,321	20,143
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,368,122	1,327,990
Available-for-Sale: Gross Unrealized Gains	1,063	9,818
Available-for-Sale: Gross Unrealized Losses	(78,035)	(18,766)
Available-for-Sale: Fair Value	1,291,150	1,319,042
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	1,681,326	1,774,394
Held-to-Maturity: Gross Unrealized Gains	3,259	12,139
Held-to-Maturity: Gross Unrealized Losses	(118,611)	(30,621)
Held-to-Maturity: Fair Value	1,565,974	1,755,912
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	2,201,086	2,127,781
Available-for-Sale: Gross Unrealized Gains	128	4,792
Available-for-Sale: Gross Unrealized Losses	(170,933)	(42,247)
Available-for-Sale: Fair Value	2,030,281	2,090,326
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	2,189,122	2,286,880
Held-to-Maturity: Gross Unrealized Gains	547	15,508
Held-to-Maturity: Gross Unrealized Losses	(152,862)	(32,627)
Held-to-Maturity: Fair Value	2,036,807	2,269,761
Commercial - Government Agencies or Sponsored Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	188,073	155,164
Available-for-Sale: Gross Unrealized Gains	24	1,885
Available-for-Sale: Gross Unrealized Losses	(7,132)	(1,159)
Available-for-Sale: Fair Value	180,965	155,890
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	468,145	481,695
Held-to-Maturity: Gross Unrealized Gains		324
Held-to-Maturity: Gross Unrealized Losses	(40,927)	(12,355)
Held-to-Maturity: Fair Value	427,218	469,664
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	3,757,281	3,610,935
Available-for-Sale: Gross Unrealized Gains	1,215	16,495
Available-for-Sale: Gross Unrealized Losses	(256,100)	(62,172)
Available-for-Sale: Fair Value	3,502,396	3,565,258
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	4,338,593	4,542,969
Held-to-Maturity: Gross Unrealized Gains	3,806	27,971
Held-to-Maturity: Gross Unrealized Losses	(312,400)	(75,603)
Held-to-Maturity: Fair Value	$ 4,029,999	$ 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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