Retirement Plans, Amounts Recognized in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Noncurrent asset	$ 0	$ 0
Current liability	0	0
Long-term liability	(59,999)	(79,659)
SERP [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Noncurrent asset	0	0
Current liability	(159)	(150)
Long-term liability	(1,253)	(1,307)
Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Noncurrent asset	0	0
Current liability	(54)	(56)
Long-term liability	$ (625)	$ (619)