DEBT - Long-term debt (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Mar. 09, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total carrying amount of debt		$ 395,783		$ 105,543
Convertible notes embedded derivative		45,100
Less: current portion of convertible notes and long-term financing receivable recorded as debt		(100,567)		(2,884)
Long-term debt	[1]	295,216		102,659
Convertible Notes | Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Long-term debt, gross		320,000		0
Less unamortized discount and issuance costs		(75,450)		0
Total carrying amount of debt		244,550		0
Convertible notes embedded derivative		45,100	$ 68,700	0
Convertible Notes | Convertible Senior Notes Due 2024
Debt Instrument [Line Items]
Long-term debt, gross		132,000		132,000
Less unamortized discount and issuance costs		(34,087)		(35,815)
Total carrying amount of debt		97,913		96,185
Convertible Notes | Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Long-term debt, gross		5,000		5,000
Less unamortized discount and issuance costs		(132)		(143)
Total carrying amount of debt		4,868		4,857
Financing Receivable | Financing Receivable Recorded as Debt
Debt Instrument [Line Items]
Long-term debt, gross		$ 3,352		$ 4,501

[1] Debt, noncurrent balance as of March 31, 2020, includes Convertible Notes due 2025 embedded derivative balance of $45.1 million. See Note 8, “Debt,” of the notes to condensed consolidated financial statements included in Part I, Item 1 of this Form 10-Q for further details.