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Investment Securities - Securities with gross unrealized losses (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Securities Held to Maturity, Gross Unrealized Losses |  |
Less Than Twelve Months |  | $ 115,297
Twelve Months or More | $ 521,313 | 317,776
Securities Held to Maturity, Fair Value |  |
Less Than Twelve Months |  | 952,682
Twelve Months or More | 2,012,400 | 1,297,486
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months | 9,475 | 197,789
Twelve Months or More | 1,076,302 | 695,584
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months | 142,319 | 2,082,068
Twelve Months or More | 4,447,652 | 3,073,871
U.S. Treasuries |  |
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 6,778
Twelve Months or More | 2,063 |
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months |  | 265,638
Twelve Months or More | 172,259 |
U.S. Government agencies |  |
Securities Held to Maturity, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 5,514
Twelve Months or More | 33,016 | 24,273
Securities Held to Maturity, Fair Value |  |
Less Than Twelve Months |  | 78,833
Twelve Months or More | 164,250 | 88,642
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 8,193
Twelve Months or More | 29,305 | 18,691
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months |  | 138,807
Twelve Months or More | 216,754 | 80,281
Residential mortgage pass-through securities issued or guaranteed by U.S. government agencies or sponsored enterprises |  |
Securities Held to Maturity, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 65,181
Twelve Months or More | 303,022 | 189,912
Securities Held to Maturity, Fair Value |  |
Less Than Twelve Months |  | 513,086
Twelve Months or More | 1,171,338 | 823,467
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months | 1 | 42,767
Twelve Months or More | 363,096 | 255,285
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months | 94 | 459,773
Twelve Months or More | 1,488,330 | 1,238,580
Residential collateralized mortgage-obligations issued by U.S. government agencies or sponsored enterprises |  |
Securities Held to Maturity, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 30,284
Twelve Months or More | 85,938 | 39,380
Securities Held to Maturity, Fair Value |  |
Less Than Twelve Months |  | 277,868
Twelve Months or More | 365,990 | 127,128
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 21,450
Twelve Months or More | 125,154 | 85,842
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months |  | 274,082
Twelve Months or More | 519,427 | 326,963
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises |  |
Securities Held to Maturity, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 14,318
Twelve Months or More | 85,773 | 51,986
Securities Held to Maturity, Fair Value |  |
Less Than Twelve Months |  | 82,895
Twelve Months or More | 269,891 | 213,387
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months | 8,606 | 17,156
Twelve Months or More | 241,801 | 181,688
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months | 64,756 | 206,228
Twelve Months or More | 879,801 | 767,002
State and municipal obligations |  |
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months | 705 | 97,084
Twelve Months or More | 258,527 | 108,799
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months | 9,860 | 616,631
Twelve Months or More | 860,725 | 391,848
Small Business Administration loan-backed securities |  |
Securities Held to Maturity, Gross Unrealized Losses |  |
Twelve Months or More | 13,564 | 12,225
Securities Held to Maturity, Fair Value |  |
Twelve Months or More | 40,931 | 44,862
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months | 163 | 2,152
Twelve Months or More | 52,272 | 44,543
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months | 67,609 | 92,535
Twelve Months or More | 284,393 | 264,933
Corporate securities. |  |
Securities Available for Sale, Gross Unrealized Losses |  |
Less Than Twelve Months |  | 2,209
Twelve Months or More | 4,084 | 736
Securities Available for Sale, Fair Value |  |
Less Than Twelve Months |  | 28,374
Twelve Months or More | $ 25,963 | $ 4,264

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