Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Other Long-Term Liabilities [Line Items]
Supplemental employees' retirement plan ("SERP")	$ 69,610	$ 97,246
Other Liabilities, Noncurrent, Total	47,636	56,415
Other Liabilities
Other Long-Term Liabilities [Line Items]
Supplemental employees' retirement plan ("SERP")	4,898	6,808
Deferred compensation	21,968	20,768
Long-term incentive plan	3,448	10,527
Noncurrent income taxes payable	3,625	3,390
Environmental remediation liability	5,313	5,525
Finance leases	4,315	5,559
Other Accrued Liabilities, Noncurrent	$ 4,069	$ 3,838