Retirement Plans, Amounts Recognized in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Pension Plan [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Current liability	$ 0	$ 0
Long-term liability	(113,557)	(84,664)
SERP [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Current liability	(159)	(159)
Long-term liability	(1,015)	(1,066)
Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Current liability	(58)	(60)
Long-term liability	$ (571)	$ (602)