Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Long-Term Liabilities [Line Items]
Supplemental employees' retirement plan (SERP)	$ 126,924	$ 156,427
Total	46,898	44,916
Other Liabilities
Other Long-Term Liabilities [Line Items]
Supplemental employees' retirement plan (SERP)	6,954	6,998
Deferred compensation	15,862	15,238
Long-term incentive plan	9,475	8,346
Noncurrent income taxes payable	3,363	2,903
Environmental remediation liability	2,602	3,763
Capital leases	4,985	2,588
Other	$ 3,657	$ 5,080