CONVERTIBLE DEBT - Narrative (Details) $ / shares in Units, $ in Thousands	Oct. 01, 2021 USD ($) day $ / shares	Jun. 02, 2020 USD ($) day $ / shares	Sep. 13, 2019 USD ($) day $ / shares	Dec. 31, 2020 USD ($) $ / shares
Debt Instrument [Line Items]
Common stock, par value (in dollars per share) | $ / shares	$ 0.001			$ 0.001
Convertible debt in mezzanine equity section	$ 1,115			$ 0
Carrying value of liability	97,563			129,507
2022 Notes
Debt Instrument [Line Items]
Debt instrument principal amount	37,707			37,707
Unamortized debt discount	849			1,357
Carrying value of liability	36,592			35,925
2022 Notes | Senior notes
Debt Instrument [Line Items]
Debt instrument principal amount	37,700	$ 37,700
Debt instrument stated percentage (as a percent)		4.375%
Common stock, par value (in dollars per share) | $ / shares		$ 0.001
Debt instrument conversion ratio		173.9978
Debt instrument conversion price (in dollars per share) | $ / shares		$ 5.75
Fair value of debt instrument		$ 44,400
Carrying amount of equity component		8,300
Convertible debt		36,000
Unamortized debt discount		$ 1,700
Carrying value of liability	$ 36,600
2022 Notes | Senior notes | Stock price greater or equal 130 percent of note conversion rate
Debt Instrument [Line Items]
Debt instrument threshold trading days | day	20	20
Debt instrument threshold consecutive trading days | day	30	30
Debt instrument threshold percentage of stock price trigger (as a percent)	130.00%	130.00%
2022 Notes | Senior notes | Note price less than 98 percent of stock price times conversion rate
Debt Instrument [Line Items]
Debt instrument threshold trading days | day		5
Debt instrument threshold consecutive trading days | day		5
Debt instrument threshold percentage of stock price trigger (as a percent)		98.00%
2024 Notes
Debt Instrument [Line Items]
Debt instrument principal amount	$ 115,500			115,500
Unamortized debt discount	15,789			19,294
Carrying value of liability	$ 97,563			$ 93,582
2024 Notes | Senior notes
Debt Instrument [Line Items]
Debt instrument principal amount			$ 115,500
Debt instrument stated percentage (as a percent)			2.00%
Common stock, par value (in dollars per share) | $ / shares			$ 0.001
Debt instrument conversion ratio			115.5001
Debt instrument conversion price (in dollars per share) | $ / shares			$ 8.66
Carrying amount of equity component			$ 24,900
2024 Notes | Senior notes | Stock price greater or equal 130 percent of note conversion rate
Debt Instrument [Line Items]
Debt instrument threshold trading days | day			20
Debt instrument threshold consecutive trading days | day			30
Debt instrument threshold percentage of stock price trigger (as a percent)			130.00%
2024 Notes | Senior notes | Note price less than 98 percent of stock price times conversion rate
Debt Instrument [Line Items]
Debt instrument threshold trading days | day			5
Debt instrument threshold consecutive trading days | day			5
Debt instrument threshold percentage of stock price trigger (as a percent)			98.00%