v3.26.1
Other Comprehensive (Loss) Income (Schedule of Components of AOCI) (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance $ 2,833,212 $ 2,601,207
Current - period other comprehensive income (loss) (10,240) 25,109
Ending Balance 2,862,869 2,658,794
Accumulated Other Comprehensive (Loss)    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance (76,183) (135,355)
Current - period other comprehensive income (loss) (10,240) 25,109
Ending Balance (86,423) (110,246)
Unrealized Losses on Available for Sale Debt Securities    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance (77,178) (144,561)
Current - period other comprehensive income (loss) (12,689) 26,724
Ending Balance (89,867) (117,837)
Post- Retirement Obligations    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance 2,854 6,147
Current - period other comprehensive income (loss) (17) (330)
Ending Balance 2,837 5,817
Unrealized Gains on Derivatives (cash flow hedges)    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning Balance (1,859) 3,059
Current - period other comprehensive income (loss) 2,466 (1,285)
Ending Balance $ 607 $ 1,774