Retirement Plans and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Summary of Retirement Plans and Other Postretirement Benefits

Information with respect to the Retirement Plans and Other Postretirement Benefits follows:

	Retirement Plans				Other Postretirement Benefits
(Dollars in thousands)	2023		2022		2023		2022
Change in benefit obligation:
Benefit obligation at beginning of year	$	47,279	$	57,698	$	2,524	$	3,536
Service cost	532		558		76		123
Interest cost	2,365		1,573		129		96
Actuarial gain (loss)	1,436		(9,776)		(427)		(1,136)
Benefits paid	(2,835)		(2,774)		(93)		(95)
Benefit obligation at end of year	$	48,777	$	47,279	$	2,209	$	2,524
Change in plan assets:
Fair value of plan assets at beginning of year	$	49,399	$	60,479	$	—	$	—
Actual return (loss) on plan assets	7,627		(8,463)		—		—
Benefits paid	(2,835)		(2,774)		(93)		(95)
Employer contribution and non-qualified benefit payments	157		157		93		95
Fair value of plan assets at end of year	$	54,348	$	49,399	$	—	$	—
Funded status	5,571		2,120		(2,209)		(2,524)
Unrecognized net actuarial loss (gain)	15,715		19,851		(784)		(371)
Net amount recognized	$	21,286	$	21,971	$	(2,993)	$	(2,895)

Components of Net Periodic Benefit Cost (Income)

Components of net periodic benefit cost (income) were as follows: 

	Retirement Plans						Other Postretirement Benefits
(Dollars in thousands)	2023		2022		2021		2023		2022		2021
Service cost	$	532	$	558	$	567	$	76	$	123	$	143
Interest cost	2,365		1,573		1,431		129		96		85
Expected loss on plan assets	(3,056)		(3,756)		(3,656)		—		—		—
Amortization of net actuarial loss (gain)	1,001		817		1,269		(16)		56		47
Net periodic benefit cost (income)	$	842	$	(808)	$	(389)	$	189	$	275	$	275

Expected Amortization Expense

(Dollars in thousands)	Retirement Plans		Other Postretirement Benefits
Expected amortization expense for 2024:
Amortization (accretion) of net actuarial loss (gain)	$	701	$	(113)

Summary of Benefit Payments Expected to be Paid

The following benefits payments, which reflect expected future service, as appropriate, are expected to be paid:

(Dollars in thousands)	Retirement Plans		Other Postretirement Benefits
For the fiscal year ending:
2024	$	3,158	$	112
2025	3,175		115
2026	3,247		120
2027	3,272		126
2028	3,284		130
Years 2029-2033	16,542		707
Total	$	32,678	$	1,310

Weighted-Average Assumptions Used to Determine Benefit Obligations

Weighted-average assumptions used to determine benefit obligations at December 31, 2023 and 2022 were as follows:

	Retirement Plans				Other Postretirement Benefits
	2023		2022		2023		2022
Assumed discount rate	5.0	%	5.2	%	5.0	%	5.2	%
Assumed salary increase rate	3%-6%		3%-6%		—		—

The benefit obligation for all plans at December 31, 2023 was based on the Pri-2012 White Collar Dataset Mortality Table with scale MP-2021 fully generational published by the Society of Actuaries. The discount rate is based on matching the Plan's projected cash flows to the spot rates in FTSE Pension Above Median Double-A Curve as of the disclosure date. The assumed salary increase considers available service years from the valuation date through the participant's normal retirement date.

Weighted-average assumptions used to determine net periodic costs for the years ended December 31, 2023 and 2022 were as follows:

	Retirement Plans				Other Postretirement Benefits
	2023		2022		2023		2022
Assumed discount rate	5.2	%	2.8	%	5.2	%	2.8	%
Assumed long-term rate of investment return	6.5	%	6.5	%	—		—
Assumed salary increase rate	3%-6%		3%-6%		—		—
Assumed cash balance interest crediting rate	4.8	%	2.6	%	—		—

Summary of Corporation's Pension Plan Asset Allocation

The Corporation's pension plan asset allocation at December 31, 2023 and 2022, by asset category was as follows:

	Percentage of Plan Assets at December 31,
	2023		2022
Asset Category:
Equity securities	64	%	62	%
Debt securities	34		36
Other	2		2
Total	100	%	100	%

Major Categories of Assets in Corporation's Pension Plan

The major categories of assets in the Corporation's pension plan at year-end are presented in the following table. Assets are segregated by the level of the valuation inputs within the fair value hierarchy described in Note 19, "Fair Value Disclosures."

	Fair Value Measurements at December 31,
(Dollars in thousands)	2023		2022
Level 1:
Mutual funds	$	35,554	$	32,982
Short-term investments	1,208		1,187
U.S. treasury bonds	243		—
Level 2:
U.S. government obligations	7,699		6,629
Corporate bonds	6,937		5,427
Certificates of deposit	2,707		3,174
Total fair value of plan assets	$	54,348	$	49,399