Other Comprehensive (Loss) Income (Components of AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,690,596	$ 1,597,703
Current - period other comprehensive (loss) income	(10,470)	16,899
Ending Balance	1,695,162	1,640,080
Accumulated Other Comprehensive (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(141,115)	(165,045)
Current - period other comprehensive (loss) income	(10,470)	16,899
Ending Balance	(151,585)	(148,146)
Unrealized Losses on Available for Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(154,489)	(186,614)
Current - period other comprehensive (loss) income	(9,957)	20,864
Ending Balance	(164,446)	(165,750)
Post- Retirement Obligations
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	3,937	1,572
Current - period other comprehensive (loss) income	(829)	(269)
Ending Balance	3,108	1,303
Unrealized Gains on Derivatives (cash flow hedges)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	9,437	19,997
Current - period other comprehensive (loss) income	316	(3,696)
Ending Balance	$ 9,753	$ 16,301