Other Comprehensive Income (Loss) (Components of AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,597,703	$ 1,697,096
Current - period other comprehensive income (loss)	16,899	(74,809)
Ending Balance	1,640,080	1,621,131
Accumulated Other Comprehensive (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(165,045)	6,863
Ending Balance	(148,146)	(67,946)
Unrealized Losses on Available for Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(186,614)	(211)
Current - period other comprehensive income (loss)	20,864	(84,971)
Ending Balance	(165,750)	(85,182)
Post- Retirement Obligations
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	1,572	2,981
Current - period other comprehensive income (loss)	(269)	(276)
Ending Balance	1,303	2,705
Unrealized Gains on Derivatives (cash flow hedges)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	19,997	4,093
Current - period other comprehensive income (loss)	(3,696)	10,438
Ending Balance	$ 16,301	$ 14,531