THE COMPANY AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Product warranty, Advertising, AOCI, ESPP (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Product warranty
Warranty period	3 years
Changes in the entity's liability for product warranty
Balance at the beginning, product warranty accrual	$ 1,474	$ 1,641
Assumed warranty liability from acquisition	0	290
New warranties issued during the period	1,459	1,727
Reversal of warranty reserves	(565)	(856)
Settlements during the period	(1,479)	(1,328)
Balance at the end, product warranty accrual	889	1,474	$ 1,641
Less: long-term portion of product warranty liability	(183)	(211)
Product warranty liability	706	1,263
Advertising
Advertising expense	$ 2,900	$ 2,100	$ 2,000