SIGNIFICANT ACCOUNTING POLICIES - Financial Instruments (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
FAIR VALUE MEASUREMENTS
Outstanding amount of debt	$ 460,956	$ 489,355
Credit Agreement
FAIR VALUE MEASUREMENTS
Outstanding amount of debt	151,900
Credit Agreement \| Term Loan
FAIR VALUE MEASUREMENTS
Outstanding amount of debt	151,875	180,000
Credit Agreement \| Term Loan B
FAIR VALUE MEASUREMENTS
Outstanding amount of debt	280,000	280,000
Credit Agreement \| Revolving Credit Facility
FAIR VALUE MEASUREMENTS
Outstanding amount of debt	5,000	0
Seller notes
FAIR VALUE MEASUREMENTS
Outstanding amount of debt	$ 5,912	11,110
Recurring basis \| Level 1 \| Money market funds
FAIR VALUE MEASUREMENTS
Market price (in dollars per share)	$ 1
Recurring basis \| Level 1 \| Money market funds \| Other current assets
FAIR VALUE MEASUREMENTS
Fair value of assets	$ 3,300	2,300
Recurring basis \| Level 3 \| Credit Agreement \| Term Loan
FAIR VALUE MEASUREMENTS
Fair value of the debt	149,400	172,600
Recurring basis \| Level 3 \| Credit Agreement \| Term Loan B
FAIR VALUE MEASUREMENTS
Fair value of the debt	283,500	278,600
Recurring basis \| Level 3 \| Credit Agreement \| Revolving Credit Facility
FAIR VALUE MEASUREMENTS
Fair value of the debt	$ 4,900	$ 0

Represents the market price equivalent the Company uses for valuation of the money market investments.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13476-108611

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- Definition

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.

+ References

No definition available.

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