FAIR VALUE MEASUREMENTS - Schedule of Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Liabilities:
Convertible notes embedded derivative	$ 45,100
Warrants liability	38,637	$ 0
Warranty obligations, current	9,678	10,078	$ 7,925
Warranty obligations, non-current	27,823	27,020	23,117
Total warranty obligations measured at fair value	37,501	37,098	$ 31,042	$ 31,294
Recurring | Level 2
Assets:
Convertible notes hedge	47,885	0
Liabilities:
Warrants liability	38,637	0
Warranty obligations, current	0	0
Warranty obligations, non-current	0	0
Total warranty obligations measured at fair value	0	0
Total liabilities measured at fair value	83,737	0
Recurring | Level 2 | Convertible Notes
Liabilities:
Convertible notes embedded derivative	45,100	0
Recurring | Level 3
Assets:
Convertible notes hedge	0	0
Liabilities:
Warrants liability	0	0
Warranty obligations, current	6,578	6,794
Warranty obligations, non-current	13,847	13,012
Total warranty obligations measured at fair value	20,425	19,806
Total liabilities measured at fair value	20,425	19,806
Recurring | Level 3 | Convertible Notes
Liabilities:
Convertible notes embedded derivative	$ 0	$ 0