Property and Equipment (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Accrumulated Depreciation	$ 319,156	$ 306,166

Amount of increase (decrease) in accumulated depreciation, depletion and amortization of property, plant and equipment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Name:	us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipmentPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration