Commitments And Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 30, 2014
Loss Contingencies [Line Items]
Commitment for property and equipment purchases	$ 100,400		$ 100,400
Loss contingency, damages awarded, value					$ 800
Insurance and claims	22,011	$ 20,669	73,858	$ 60,336
Loss contingency, damages awarded, attorney fees and costs					$ 500
May 17, 2018 Verdict [Member]
Loss Contingencies [Line Items]
Loss contingency, damages awarded, value	92,000
Self insurance retained liability						$ 10,000
Insurance and claims			14,000
Loss contingency, receivable, noncurrent	79,200		79,200
Loss contingency, accrual, noncurrent	$ 79,200		$ 79,200