INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax [Line Items]
Unrecognized tax positions	$ 162,000	$ 187,000	$ 0	$ 0	$ 400,000
Minimum tax and research and development tax credit carryforwards	500,000
Tax reform, decrease to valuation allowance	700,000
Deferred tax asset, Valuation allowance	132,712,000	164,865,000	148,310,000	$ 136,017,000
Interest and penalties accrued (less than)	100,000	$ 100,000	$ 0
U.S. Tax Authority
Income Tax [Line Items]
Net operating loss carryforwards	334,600,000
Operating loss carryforwards deduction of stock-based compensation	27,700,000
Deferred tax asset, Valuation allowance	127,200,000
Foreign Tax Authority
Income Tax [Line Items]
Net operating loss carryforwards	37,800,000
Deferred tax asset, Valuation allowance	$ 5,500,000