FAIR VALUE MEASUREMENTS - Summary of Significant Unobservable Inputs used in the Fair Value Measurement of Liabilities Designated as Level 3 (Details) - Recurring - Level 3 - Warranty obligations for microinverters sold since January 1, 2014	Mar. 31, 2019	Dec. 31, 2018
Measurement Input, Profit Element and Risk Premium
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warranty obligations for microinverters sold since January 1, 2014	0.14	0.16
Measurement Input, Entity Credit Risk
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warranty obligations for microinverters sold since January 1, 2014	0.18	0.19