v3.25.1
Other Comprehensive (Loss) Income (Schedule of Components of AOCI) (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance $ 2,601,207 $ 1,690,596
Current - period other comprehensive income (loss) 25,109 (10,470)
Ending Balance 2,658,794 1,695,162
Accumulated Other Comprehensive (Loss)    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance (135,355) (141,115)
Current - period other comprehensive income (loss) 25,109 (10,470)
Ending Balance (110,246) (151,585)
Unrealized Losses on Available for Sale Debt Securities    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance (144,561) (154,489)
Current - period other comprehensive income (loss) 26,724 (9,957)
Ending Balance (117,837) (164,446)
Post- Retirement Obligations    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance 6,147 3,937
Current - period other comprehensive income (loss) (330) (829)
Ending Balance 5,817 3,108
Unrealized Gains on Derivatives (cash flow hedges)    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance 3,059 9,437
Current - period other comprehensive income (loss) (1,285) 316
Ending Balance $ 1,774 $ 9,753