Revenue Impact of ASC 606 in Current Period Balance Sheet (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	[1]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	$ 26,306	$ 41,286
Increase (Decrease) in Prepaid Expense and Other Assets	566
Accrued liabilities	131,954	132,064
Increase (Decrease) in Accrued Liabilities	8,153
DEFERRED INCOME TAXES	20,341	$ 24,775
Deferred Tax Liabilities, Tax Deferred Income	1,999
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	26,872
Accrued liabilities	140,107
DEFERRED INCOME TAXES	$ 22,340

[1] December 31, 2017 balances were derived from audited consolidated financial statements.