Securities - Schedule of Changes in Equity Securities Without Readily Determinable Fair Values (Detail) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Equity Securities, FV-NI and without Readily Determinable Fair Value [Abstract] | ||||
| Beginning balance | $ 535,326 | $ 539,930 | $ 524,112 | $ 416,750 |
| Acquisition of HTLF | 1,117 | 122,886 | ||
| Purchases of securities | 16,322 | 24,827 | 49,986 | 48,830 |
| Observable upward price adjustments | 30,902 | 9,411 | 34,470 | 10,433 |
| Observable downward price adjustments | (4,088) | (2,302) | (4,724) | (8,575) |
| Sales of securities and other activity | (35,237) | (39,234) | (60,619) | (56,575) |
| Ending balance | $ 543,225 | $ 533,749 | $ 543,225 | $ 533,749 |