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Investment Securities - Gross Unrealized Losses on Debt Securities (Detail) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Debt Securities Available for Sale |  |
Less than 12 months, fair value | $ 64,135 | $ 117,107
Less than 12 months, unrealized loss | (548) | (1,029)
12 months or more, fair value | 1,353,929 | 1,546,730
12 months or more, unrealized loss | (167,607) | (233,626)
Total, fair value | 1,418,064 | 1,663,837
Total, unrealized loss | (168,155) | (234,655)
Debt Securities Held to Maturity |  |
Less than 12 months, fair value | 0 | 0
Less than 12 months, unrealized loss | 0 | 0
12 months or more, fair value | 91,139 | 103,038
12 months or more, unrealized loss | (4,150) | (7,522)
Total, fair value | 91,139 | 103,038
Total, unrealized loss | (4,150) | (7,522)
Obligations of U.S. government agencies |  |
Debt Securities Available for Sale |  |
Less than 12 months, fair value | 24,696 | 63,714
Less than 12 months, unrealized loss | (292) | (842)
12 months or more, fair value | 938,888 | 1,021,654
12 months or more, unrealized loss | (121,885) | (173,643)
Total, fair value | 963,584 | 1,085,368
Total, unrealized loss | (122,177) | (174,485)
Debt Securities Held to Maturity |  |
Less than 12 months, fair value | 0 | 0
Less than 12 months, unrealized loss | 0 | 0
12 months or more, fair value | 89,587 | 101,553
12 months or more, unrealized loss | (4,138) | (7,443)
Total, fair value | 89,587 | 101,553
Total, unrealized loss | (4,138) | (7,443)
Obligations of states and political subdivisions |  |
Debt Securities Available for Sale |  |
Less than 12 months, fair value | 4,090 | 7,457
Less than 12 months, unrealized loss | (123) | (140)
12 months or more, fair value | 206,521 | 208,063
12 months or more, unrealized loss | (22,648) | (28,809)
Total, fair value | 210,611 | 215,520
Total, unrealized loss | (22,771) | (28,949)
Debt Securities Held to Maturity |  |
Less than 12 months, fair value | 0 | 0
Less than 12 months, unrealized loss | 0 | 0
12 months or more, fair value | 1,552 | 1,485
12 months or more, unrealized loss | (12) | (79)
Total, fair value | 1,552 | 1,485
Total, unrealized loss | (12) | (79)
Corporate bonds |  |
Debt Securities Available for Sale |  |
Less than 12 months, fair value | 497 | 1,229
Less than 12 months, unrealized loss | (1) | (17)
12 months or more, fair value | 2,650 | 4,608
12 months or more, unrealized loss | (65) | (328)
Total, fair value | 3,147 | 5,837
Total, unrealized loss | (66) | (345)
Asset backed securities |  |
Debt Securities Available for Sale |  |
Less than 12 months, fair value | 24,169 | 44,707
Less than 12 months, unrealized loss | (128) | (30)
12 months or more, fair value | 71,006 | 75,734
12 months or more, unrealized loss | (1,590) | (1,208)
Total, fair value | 95,175 | 120,441
Total, unrealized loss | (1,718) | (1,238)
Non-agency collateralized mortgage obligations |  |
Debt Securities Available for Sale |  |
Less than 12 months, fair value | 10,683 | 0
Less than 12 months, unrealized loss | (4) | 0
12 months or more, fair value | 134,864 | 236,671
12 months or more, unrealized loss | (21,419) | (29,638)
Total, fair value | 145,547 | 236,671
Total, unrealized loss | $ (21,423) | $ (29,638)

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