Revenue Impact of ASC 606 in Current Period Balance Sheet (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	[1]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	$ 28,742	$ 41,286
Increase (Decrease) in Prepaid Expense and Other Assets	4,143
Accrued liabilities	111,280	132,064
Increase (Decrease) in Accrued Liabilities	21,656
DEFERRED INCOME TAXES	19,584	$ 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	32,885
Accrued liabilities	132,936
DEFERRED INCOME TAXES	$ 21,583

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