INCOME TAXES (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Adjustment to deferred tax assets as a result of Tax Reform Act	$ 3,800
Cumulative earnings which federal tax has not been provided	2,300
Unrecognized tax benefits	18,215	$ 10,340	$ 5,049	$ 3,276
Unrecognized tax benefits that would impact effective tax rate	900
California Enterprise Zone Credit
Income Taxes [Line Items]
Credit carryforwards	2,600
Domestic
Income Taxes [Line Items]
Net operating loss carryforwards	17,700
Domestic | Research
Income Taxes [Line Items]
Credit carryforwards	7,400
State
Income Taxes [Line Items]
Net operating loss carryforwards	35,800
State | Research
Income Taxes [Line Items]
Credit carryforwards	22,900
GERMANY
Income Taxes [Line Items]
Net operating loss carryforwards	$ 7,600