Revenue Impact of ASC 606 in Current Period Balance Sheet (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	[1]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	$ 32,406,000	$ 41,286,000
Increase (Decrease) in Prepaid Expense and Other Assets	3,123,000
Accrued liabilities	116,448,000	132,064,000
Increase (Decrease) in Accrued Liabilities	13,484,000
DEFERRED INCOME TAXES	20,073,000	$ 24,775,000
Deferred Tax Liabilities, Tax Deferred Income	1,999,000
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	35,529,000
Accrued liabilities	129,932,000
DEFERRED INCOME TAXES	$ 22,072,000

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