Pension Plan and Postretirement Benefits Other Than Pension - Changes in net funded status, disclosure of amounts recognized in the balance sheet, and the assumptions used to determine the benefit (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amounts recognized in the statement of financial position:
Noncurrent liabilities		$ (446)	$ (3,145)
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Final number of years of employee's compensation to determine the benefits payable		10 years
Settlement loss		$ 1,302
Change in projected benefit obligation:
Net benefit obligation at beginning of year		186,480	154,528	$ 184,245
Interest cost		3,070	6,146	5,986
Benefits paid		(1,154)	(13,221)	(13,690)
Actuarial loss (gain)		9,294	39,027	(22,013)
Plan Termination		(197,690)
Net benefit obligation at end of year			186,480	154,528
Change in plan assets:
Fair value of plan assets at beginning of year		183,903	162,999	170,881
Actual return on plan assets		11,378	34,125	1,808
Employer contributions	$ 3,700	3,661	0	4,000
Benefits paid		(1,154)	(13,221)	(13,690)
Plan Termination		$ (197,788)
Fair value of plan assets at end of year			183,903	162,999
Funded status at end of year			(2,577)	8,471
Amounts recognized in the statement of financial position:
Noncurrent assets				8,471
Noncurrent liabilities			(2,577)
Net amount recognized at end of year			$ (2,577)	$ 8,471
Weighted average assumptions used to determine benefit obligation at December 31:
Discount rate (as a percent)			3.32%	4.45%
Other Postretirement Benefits
Pension Plan and Postretirement Benefits Other than Pension
Age of employees after which the plan does not provide benefits		65 years
Change in projected benefit obligation:
Net benefit obligation at beginning of year		$ 726	$ 1,048	$ 2,195
Interest cost		15	33	54
Benefits paid		(827)	(677)	(602)
Actuarial loss (gain)		409	47	(965)
Retiree contributions		220	275	366
Net benefit obligation at end of year		543	726	1,048
Change in plan assets:
Employer contributions		607	402	236
Retiree contributions		220	275	366
Benefits paid		(827)	(677)	(602)
Funded status at end of year		(543)	(726)	(1,048)
Amounts recognized in the statement of financial position:
Current liabilities		(97)	(158)	(250)
Noncurrent liabilities		(446)	(568)	(798)
Net amount recognized at end of year		$ (543)	$ (726)	$ (1,048)
Weighted average assumptions used to determine benefit obligation at December 31:
Discount rate (as a percent)		2.03%	2.87%	4.08%