Securities Available for Sale and Held to Maturity - Securities with Gross Unrealized Losses, Segregated by Length of Impairment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 2,845,840	$ 2,423,465
Estimated Fair Value, 12 Months or More	602,217	67,875
Estimated Fair Value, Total	3,448,057	2,491,340
Gross Unrealized (Losses), Less than 12 Months	(143,228)	(29,552)
Gross Unrealized (Losses), 12 Months or More	(44,509)	(1,406)
Gross Unrealized (Losses), Total	(187,737)	(30,958)
US Treasury Securities [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	361,822	315,123
Estimated Fair Value, 12 Months or More	0	0
Estimated Fair Value, Total	361,822	315,123
Gross Unrealized (Losses), Less than 12 Months	(22,312)	(4,938)
Gross Unrealized (Losses), 12 Months or More	0	0
Gross Unrealized (Losses), Total	(22,312)	(4,938)
U.S. Government Agency Obligations [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	3,501	1,312
Estimated Fair Value, 12 Months or More	8,252	8,619
Estimated Fair Value, Total	11,753	9,931
Gross Unrealized (Losses), Less than 12 Months	(172)	(5)
Gross Unrealized (Losses), 12 Months or More	(316)	(332)
Gross Unrealized (Losses), Total	(488)	(337)
Obligations of States and Political Subdivisions [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	0	3,006
Estimated Fair Value, 12 Months or More	3,669	667
Estimated Fair Value, Total	3,669	3,673
Gross Unrealized (Losses), Less than 12 Months	0	(1)
Gross Unrealized (Losses), 12 Months or More	(4)	(2)
Gross Unrealized (Losses), Total	(4)	(3)
Residential Mortgage Pass-Through Securities Guaranteed by GNMA [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	35,599	6,040
Estimated Fair Value, 12 Months or More	57	0
Estimated Fair Value, Total	35,656	6,040
Gross Unrealized (Losses), Less than 12 Months	(1,249)	(37)
Gross Unrealized (Losses), 12 Months or More	(1)	0
Gross Unrealized (Losses), Total	(1,250)	(37)
Residential Mortgage Pass-Through Securities Issued by FNMA and FHLMC [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,644,138	1,734,921
Estimated Fair Value, 12 Months or More	563,850	55,303
Estimated Fair Value, Total	2,207,988	1,790,224
Gross Unrealized (Losses), Less than 12 Months	(82,266)	(19,980)
Gross Unrealized (Losses), 12 Months or More	(41,943)	(1,034)
Gross Unrealized (Losses), Total	(124,209)	(21,014)
Other Residential Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	313,741	19,038
Estimated Fair Value, 12 Months or More	1,397	2,647
Estimated Fair Value, Total	315,138	21,685
Gross Unrealized (Losses), Less than 12 Months	(6,727)	(99)
Gross Unrealized (Losses), 12 Months or More	(18)	(29)
Gross Unrealized (Losses), Total	(6,745)	(128)
Commercial Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Estimated Fair Value, Less than 12 Months	487,039	344,025
Estimated Fair Value, 12 Months or More	24,992	639
Estimated Fair Value, Total	512,031	344,664
Gross Unrealized (Losses), Less than 12 Months	(30,502)	(4,492)
Gross Unrealized (Losses), 12 Months or More	(2,227)	(9)
Gross Unrealized (Losses), Total	$ (32,729)	$ (4,501)