WARRANTY OBLIGATIONS - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Product Warranty Liability [Line Items]
Warranty obligations, end of period	$ 30,349	$ 30,066	$ 30,500	$ 32,806	$ 33,763	$ 33,940
Recurring | Warranty obligations for microinverters sold since January 1, 2014 | Level 3
Product Warranty Liability [Line Items]
Fair value liabilities	$ 9,515	$ 8,053	$ 6,182	$ 6,816	$ 5,803	$ 3,562