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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Risk (Details) - Customer concentration - customer	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Credit concentrations and significant customers
Number of customers	1	2	2
Revenues | Customer One
Credit concentrations and significant customers
Percentage of concentration risk	11.00%	13.00%	14.00%
Revenues | Customer Two
Credit concentrations and significant customers
Percentage of concentration risk		10.00%	12.00%
Accounts receivable
Credit concentrations and significant customers
Number of customers	0	1
Percentage of concentration risk	10.00%	18.00%

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- Definition

Represents the number customers of the entity from which revenue was earned.

+ References

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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.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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