THE COMPANY AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and equipment (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Property and equipment, net:
Cost and accumulated depreciation, period increase (decrease)	$ 72.8
Computer, equipment, and software
Property and equipment, net:
Property, plant and equipment, useful life	3 years
Lab equipment
Property and equipment, net:
Property, plant and equipment, useful life	7 years
Office furnitures and fixtures
Property and equipment, net:
Property, plant and equipment, useful life	7 years