GEOGRAPHIC AND CUSTOMER CONCENTRATION INFORMATION - Summary of Net Revenue by Geographic Areas Based on the Installation Locations of the Systems and the Location of Services Rendered (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 31, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 54,747	$ 38,430	$ 42,029	$ 43,198	$ 40,783	$ 33,840	$ 24,574	$ 20,237	$ 178,404	$ 119,434	$ 126,526
Geographic concentration risk | Net revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage									100.00%	100.00%	99.50%
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									25,716	12,350	17,476
United States | Geographic concentration risk | Net revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage									14.00%	10.00%	14.00%
Korea
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									87,585	22,173	47,611
Korea | Geographic concentration risk | Net revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage									49.00%	19.00%	38.00%
Taiwan
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									32,304	50,782	28,577
Taiwan | Geographic concentration risk | Net revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage									18.00%	43.00%	23.00%
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									17,369	20,250	8,562
China | Geographic concentration risk | Net revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage									10.00%	17.00%	7.00%
Other Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									6,869	8,740	13,615
Other Asia | Geographic concentration risk | Net revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage									4.00%	7.00%	10.00%
Europe and others
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									$ 8,561	$ 5,139	$ 10,685
Europe and others | Geographic concentration risk | Net revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage									5.00%	4.00%	8.00%