DEBT - Long-term debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total carrying amount of debt	$ 1,026,283	$ 330,865
Less: current portion of convertible notes and long-term financing receivable recorded as debt	(86,039)	(325,967)
Long-term debt	940,244	4,898
Convertible Notes \| Convertible Senior Notes Due 2028
Debt Instrument [Line Items]
Long-term debt, gross	575,000	0
Less unamortized discount and issuance costs	(154,636)	0
Total carrying amount of debt	420,364	0
Convertible Notes \| Convertible Senior Notes Due 2026
Debt Instrument [Line Items]
Long-term debt, gross	632,500	0
Less unamortized discount and issuance costs	(117,548)	0
Total carrying amount of debt	514,952	0
Convertible Notes \| Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Long-term debt, gross	102,175	320,000
Less unamortized discount and issuance costs	(17,306)	(64,979)
Total carrying amount of debt	84,869	255,021
Less: current portion of convertible notes and long-term financing receivable recorded as debt	(102,200)
Convertible Notes \| Convertible Senior Notes Due 2024
Debt Instrument [Line Items]
Long-term debt, gross	1,068	88,140
Less unamortized discount and issuance costs	(185)	(19,119)
Total carrying amount of debt	883	69,021
Less: current portion of convertible notes and long-term financing receivable recorded as debt	(900)
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	(72)	(102)
Total carrying amount of debt	4,928	4,898
Financing Receivable \| Financing Receivable Recorded as Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 287	$ 1,925

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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