Other Comprehensive Income (Loss) (Activity in Other Comprehensive Income) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Change in fair value of securities available for sale, before tax		$ 20,163		$ (163,471)		$ (21,942)
Change in fair value of securities available for sale, tax benefit (expense)		(5,721)		39,233		5,266
Change is fair value of securities available for sale		14,442		(124,238)		(16,676)
Change in fair value of cash flow hedges, before tax		1,647		(27,344)		(3,067)
Change in fair value of cash flow hedges, tax benefit (expense)		(346)		6,563		736
Change in fair value of cash flow hedges		1,301		(20,781)		(2,331)
Net losses (gains) on cash flow hedges reclassified into earnings, before tax		7,563	[1]	2,828	[2]	(310)	[3]
Net losses (gains) on cash flow hedges reclassified into earnings, tax benefit (expense)		(1,838)	[1]	(679)	[2]	75	[3]
Net losses (gains) on cash flow hedges reclassified into earnings		5,725	[1]	2,149	[2]	(235)	[3]
Net change in the fair value of cash flow hedges, before tax		9,210		(24,516)		(3,377)
Net change in the fair value of cash flow hedges, tax benefit (expense)		(2,184)		5,884		811
Net change in fair value of cash flow hedges		7,026		(18,632)		(2,566)
Defined benefit plan obligation adjustment, before tax		(6,712)		4,934		5,908
Defined benefit plan obligation adjustment, tax benefit (expense)		1,712		(1,184)		(1,417)
Defined benefit plan obligation adjustment		(5,000)		3,750		4,491
Amortization of net actuarial losses, before tax	[4]	237		1,712		2,844
Amortization of net actuarial losses, tax benefit (expense)	[4]	(58)		(411)		(683)
Amortization of net actuarial losses	[4]	179		1,301		2,161
Net change in defined benefit plan obligations, before tax		(6,475)		6,646		8,752
Net change in defined benefit plan obligations, tax benefit (expense)		1,654		(1,595)		(2,100)
Net change in defined benefit plan obligations		(4,821)		5,051		6,652
Total other comprehensive income (loss), before tax		22,898		(181,341)		(16,567)
Total other comprehensive income (loss), tax benefit (expense)		(6,251)		43,522		3,977
Total other comprehensive income (loss), net of tax		16,647		(137,819)		(12,590)
Federal Home Loan Bank of Boston [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net losses (gains) on cash flow hedges reclassified into earnings, before tax		(1,700)		70		1,100
Interest Income [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net losses (gains) on cash flow hedges reclassified into earnings, before tax		$ 9,200		$ 2,800		$ (1,500)

[1] The pre-tax amounts reclassified into earnings in the Consolidated Statements of Income include a $9.2 million reduction in interest and fees on loans and a $1.7 million reduction in FHLB interest expense.

[2] The pre-tax amounts reclassified into earnings in the Consolidated Statements of Income include a $2.8 million reduction in interest and fees on loans and a $70 thousand increase in FHLB interest expense.

[3] The pre-tax amounts reclassified into earnings in the Consolidated Statements of Income include a $1.5 million increase in interest and fees on loans and a $1.1 million increase in FHLB interest expense.

[4] The pre-tax amount presented above is included in other expenses in the Consolidated Statements of Income.