NEW ACCOUNTING STANDARDS IMPLMEMENTED (Details) - USD ($)	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liabilities [Abstract]
Current portion of deferred revenue	$ 296,000	$ 0	$ 3,214,000
Total current liabilities	20,354,000	2,393,000	5,607,000
Deferred revenue, net of current portion	0	0	3,061,000
Total liabilities	40,354,000	2,393,000	8,668,000
Stockholders' Equity Attributable to Parent [Abstract]
Accumulated deficit	(410,188,000)	(353,517,000)	(359,792,000)
Total stockholders' equity	134,045,000	$ 176,373,000	170,098,000	$ 99,098,000	$ 67,721,000
Scenario Previously Reported
Liabilities [Abstract]
Current portion of deferred revenue	6,308,000		3,214,000
Total current liabilities	26,366,000		5,607,000
Deferred revenue, net of current portion	2,460,000		3,061,000
Total liabilities	48,826,000		8,668,000
Stockholders' Equity Attributable to Parent [Abstract]
Accumulated deficit	(412,382,000)		(359,792,000)
Total stockholders' equity	131,851,000		170,098,000
Scenario Adjustment
Liabilities [Abstract]
Current portion of deferred revenue	(6,012,000)		(3,214,000)
Total current liabilities	(6,012,000)		(3,214,000)
Deferred revenue, net of current portion	(2,460,000)		(3,061,000)
Total liabilities	(8,472,000)		(6,275,000)
Stockholders' Equity Attributable to Parent [Abstract]
Accumulated deficit	2,194,000		6,275,000
Total stockholders' equity	$ 2,194,000		$ 6,275,000