Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 3,109,778	$ 3,172,436
Available-for-Sale: Gross Unrealized Gains	2,378	1,851
Available-for-Sale: Gross Unrealized Losses	(297,073)	(329,464)
Available-for-Sale: Fair Value	2,815,083	2,844,823
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	5,312,815	5,414,139
Held-to-Maturity: Gross Unrealized Gains	103	43
Held-to-Maturity: Gross Unrealized Losses	(711,042)	(798,789)
Held-to-Maturity: Fair Value	4,601,876	4,615,393
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	240,400	248,335
Available-for-Sale: Gross Unrealized Gains	535	638
Available-for-Sale: Gross Unrealized Losses	(12,564)	(15,067)
Available-for-Sale: Fair Value	228,371	233,906
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	131,649	131,619
Held-to-Maturity: Gross Unrealized Losses	(15,407)	(18,202)
Held-to-Maturity: Fair Value	116,242	113,417
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	107,659	107,689
Available-for-Sale: Gross Unrealized Gains	458	158
Available-for-Sale: Gross Unrealized Losses	(10,375)	(12,582)
Available-for-Sale: Fair Value	97,742	95,265
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	48,807	48,807
Available-for-Sale: Gross Unrealized Gains		0
Available-for-Sale: Gross Unrealized Losses	(151)	(179)
Available-for-Sale: Fair Value	48,656	48,628
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	849,661	850,585
Available-for-Sale: Gross Unrealized Gains	1,148	809
Available-for-Sale: Gross Unrealized Losses	(51,776)	(56,736)
Available-for-Sale: Fair Value	799,033	794,658
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	12,397	17,014
Held-to-Maturity: Gross Unrealized Losses	(2,010)	(2,534)
Held-to-Maturity: Fair Value	10,387	14,480
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	799,732	828,798
Available-for-Sale: Gross Unrealized Gains	235	245
Available-for-Sale: Gross Unrealized Losses	(86,385)	(96,215)
Available-for-Sale: Fair Value	713,582	732,828
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	1,807,744	1,848,239
Held-to-Maturity: Gross Unrealized Gains	58	35
Held-to-Maturity: Gross Unrealized Losses	(253,255)	(294,047)
Held-to-Maturity: Fair Value	1,554,547	1,554,227
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	896,586	919,980
Available-for-Sale: Gross Unrealized Gains	2	1
Available-for-Sale: Gross Unrealized Losses	(113,989)	(126,110)
Available-for-Sale: Fair Value	782,599	793,871
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	2,916,693	2,968,322
Held-to-Maturity: Gross Unrealized Gains	45	8
Held-to-Maturity: Gross Unrealized Losses	(356,166)	(397,055)
Held-to-Maturity: Fair Value	2,560,572	2,571,275
Commercial - Government Agencies or Sponsored Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	166,933	168,242
Available-for-Sale: Gross Unrealized Losses	(21,833)	(22,575)
Available-for-Sale: Fair Value	145,100	145,667
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	444,332	448,945
Held-to-Maturity: Gross Unrealized Losses	(84,204)	(86,951)
Held-to-Maturity: Fair Value	360,128	361,994
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,863,251	1,917,020
Available-for-Sale: Gross Unrealized Gains	237	246
Available-for-Sale: Gross Unrealized Losses	(222,207)	(244,900)
Available-for-Sale: Fair Value	1,641,281	1,672,366
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	5,168,769	5,265,506
Held-to-Maturity: Gross Unrealized Gains	103	43
Held-to-Maturity: Gross Unrealized Losses	(693,625)	(778,053)
Held-to-Maturity: Fair Value	$ 4,475,247	$ 4,487,496

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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