Other Comprehensive Income (Loss) (Activity in Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Changes in fair value of available for sale debt securities, before tax		$ 17,365	$ (65,078)
Changes in fair value of available for sale debt securities, tax		(4,167)	15,618
Changes in fair value of available for sale debt securities, net of tax		13,198	(49,460)
Changes in fair value of cash flow hedges, before tax		1,046	(13,201)
Changes in fair value of cash flow hedges, tax		(251)	3,168
Change in fair value of cash flow hedges , net of tax		795	(10,033)
Net cash flow hedge (gains) losses reclassified into earnings, before tax	[1]	2,636	(399)
Net cash flow hedge (gains) losses reclassified into earnings, tax		(634)	97
Net cash flow hedge (gains) losses reclassified into earnings, net of tax		2,002	(302)
Net change in fair value of cash flow hedges, before tax		3,682	(13,600)
Net change in fair value of cash flow hedges, tax		(885)	3,265
Net change in fair value of cash flow hedges, net of tax		2,797	(10,335)
Amortization of net actuarial losses, before tax	[2]	59	428
Amortization of net actuarial losses, tax		(14)	(103)
Amortization of net actuarial losses, net of tax		45	325
Total other comprehensive income (loss), before tax		21,106	(78,250)
Total other comprehensive income (loss), tax		(5,066)	18,780
Total other comprehensive income (loss), net of tax		16,040	(59,470)
Federal Home Loan Bank of Boston [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net cash flow hedge (gains) losses reclassified into earnings, before tax		(127)	94
Interest Income
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net cash flow hedge (gains) losses reclassified into earnings, before tax		$ 2,800	$ (493)

[1] For the three months ended March 31, 2023 and 2022, the pre-tax amounts reclassified into earnings in the Unaudited Consolidated Statements of Income include a reduction of $2.8 million and an increase of $493 thousand, respectively, in interest and fees on loans, as well as a reduction of $127 thousand and an increase of $94 thousand, respectively, in FHLB interest expense.

[2] The pre-tax amounts are included in other expenses in the Unaudited Consolidated Statements of Income.