Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e1043-128460

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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- Definition

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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ACQUISITIONS Table 2 - Certain Financial Information Related to the Navigator Acquisition (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Revenues	$ 450,535	$ 440,566	$ 435,488	$ 487,430	$ 471,757	$ 441,418	$ 437,804	$ 405,703	$ 1,814,019	$ 1,756,682	$ 2,084,040
Operating income (loss)	$ 74,018	$ 91,717	$ 73,404	$ 97,139	$ 85,373	$ 87,954	$ 91,217	$ 94,565	336,278	$ 359,109	$ 390,704
Navigator Acquisition [Member]
Business Acquisition [Line Items]
Revenues									42,620
Operating income (loss)									(1,724)
Business acquisition, transaction costs									14,079
Navigator Acquisition [Member] \| General and administrative expense [Member]
Business Acquisition [Line Items]
Business acquisition, transaction costs									10,391
Navigator Acquisition [Member] \| Interest expense, net [Member]
Business Acquisition [Line Items]
Business acquisition, transaction costs									$ 3,688