INCOME TAXES - Valuation allowance (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowance - beginning of year	$ 41,100	$ 40,331
Valuation allowance - end of year	16,157	41,100
Operating loss carryforwards
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	(27,116)	3,857
Foreign tax credit
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	267	(2,775)
Australian CTA and accruals and other foreign rate differentials
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	1,006	(313)
Change in investment-related items
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	900	$ 0
Items unrelated to Australian operations
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	$ (1,200)

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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- Definition

Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32123-109318

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