SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Purchased and Internally Developed Software (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Less accumulated amortization	$ (122,283)	$ (87,486)
Net	141,110	157,050
Software
Finite-Lived Intangible Assets [Line Items]
Less accumulated amortization	(54,194)	(47,957)
Net	26,776	27,303
Software \| Purchased software
Finite-Lived Intangible Assets [Line Items]
Software	25,805	23,753
Software \| Internally developed software
Finite-Lived Intangible Assets [Line Items]
Software	$ 55,165	$ 51,507

Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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