INVESTMENTS AND FAIR VALUE MEASUREMENTS - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets:
Total	$ 47,145	$ 12,367
Quoted Prices in Active Market (Level 1)
Assets:
Total	42,589	8,111
Significant Other Observable Inputs (Level 2)
Assets:
Total	4,556	4,256
Significant Unobservable Inputs (Level 3)
Assets:
Total	0	0
Fair Value, Measurements, Recurring \| Money market funds
Assets:
Cash equivalents	10,973	8,111
Fair Value, Measurements, Recurring \| Money market funds \| Quoted Prices in Active Market (Level 1)
Assets:
Cash equivalents	10,973	8,111
Fair Value, Measurements, Recurring \| Money market funds \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Fair Value, Measurements, Recurring \| Money market funds \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Money market funds \| Fair Value, Measurements, Recurring
Assets:
Funds held for clients	31,616	0
Money market funds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Market (Level 1)
Assets:
Funds held for clients	31,616	0
Money market funds \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Funds held for clients	0	0
Money market funds \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Funds held for clients	0	0
Short-term available-for-sale securities \| Fair Value, Measurements, Recurring
Assets:
Funds held for clients	4,556	4,256
Short-term available-for-sale securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Market (Level 1)
Assets:
Funds held for clients	0	0
Short-term available-for-sale securities \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Funds held for clients	4,556	4,256
Short-term available-for-sale securities \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Funds held for clients	$ 0	$ 0

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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