Other Comprehensive Income (Loss) (Components of AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,697,096	$ 1,619,797
Current - period other comprehensive (loss)	(74,809)	(4,678)
Ending Balance	1,621,131	1,647,231
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	6,863	17,655
Ending Balance	(67,946)	12,977
Unrealized Losses on Available for Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(211)	23,690
Current - period other comprehensive (loss)	(84,971)	(9,190)
Ending Balance	(85,182)	14,500
Post- Retirement Obligations
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	2,981	(1,081)
Current - period other comprehensive (loss)	(276)	(109)
Ending Balance	2,705	(1,190)
Unrealized Gains on Derivatives (cash flow hedges)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	4,093	(4,954)
Current - period other comprehensive (loss)	10,438	4,621
Ending Balance	$ 14,531	$ (333)