DEBT (Convertible Senior Notes) (Details)			3 Months Ended	12 Months Ended
	Jul. 24, 2020 USD ($) day $ / shares Rate shares	May 31, 2017 USD ($) day segment $ / shares Rate shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Rate	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Repayments of convertible debt				$ 233,862,000	$ 0	$ 0
Amortization of convertible debt discount				19,570,000	12,016,000	11,397,000
Amortization of debt issuance costs				3,474,000	1,974,000	1,776,000
Debt Issuance Costs, Net [Abstract]
Net carrying amount				$ 611,412,000	264,391,000
2025 Convertible Notes
Debt Instrument [Line Items]
Interest rate	0.50%			0.50%
Conversion rate, number of shares per $1,000 of principal | shares	2.1683
Conversion price (in dollars per share) | $ / shares	$ 461.19
Threshold percentage of stock price trigger | Rate	130.00%			130.00%
Redemption percentage | Rate	100.00%
Nonconvertible debt borrowing rate at the date of issuance | Rate	5.30%
Convertible debt, noncurrent	$ 455,600,000
Carrying amount of debt, equity component	119,400,000
Debt issuance costs, gross	15,100,000
Debt issuance costs, liability component	12,000,000.0			$ 11,056,000
Debt issuance costs, equity component	$ 3,100,000
Interest expense				11,500,000
Interest expense, excluding amortization				$ 1,300,000
Interest rate	0.50%			0.50%
Amortization of convertible debt discount				$ 9,300,000
Amortization of debt issuance costs				900,000
Debt Issuance Costs, Net [Abstract]
Gross carrying amount				575,000,000
Unamortized debt discount				110,110,000
Debt issuance costs	$ 12,000,000.0			11,056,000
Net carrying amount				453,834,000
2025 Convertible Notes | Conversion option one
Debt Instrument [Line Items]
Threshold trading days | day	20
Threshold consecutive trading days | day	30
Threshold percentage of stock price trigger | Rate	130.00%
2025 Convertible Notes | Conversion option two
Debt Instrument [Line Items]
Threshold trading days | day	5
Threshold consecutive trading days | day	5
Threshold percentage of stock price trigger | Rate	98.00%
2025 Convertible Notes | Convertible Debt
Debt Instrument [Line Items]
Aggregate principal amount	$ 575,000,000.0
Interest rate | Rate	0.50%
Long-term debt, fair value				$ 564,100,000
2025 Notes Under 13-day Purchase Option | Convertible Debt
Debt Instrument [Line Items]
Aggregate principal amount	$ 75,000,000.0
2022 Convertible Notes
Debt Instrument [Line Items]
Aggregate principal amount		$ 300,000,000.0
Interest rate		0.625%		0.625%
Conversion rate, number of shares per $1,000 of principal | shares		4.8163
Conversion price (in dollars per share) | $ / shares		$ 207.63
Threshold percentage of stock price trigger		130.00%
Redemption percentage		100.00%
Nonconvertible debt borrowing rate at the date of issuance		5.36%
Convertible debt, noncurrent		$ 238,400,000
Carrying amount of debt, equity component		61,600,000
Debt issuance costs, gross		9,300,000
Debt issuance costs, liability component		7,400,000		$ 1,297,000	3,811,000
Debt issuance costs, equity component		1,900,000
Repayments of convertible debt	234,000,000.0
Repurchased face amount	130,300,000
Repurchased amount, accrued interest	100,000
Extinguishment of debt	126,000,000.0
Repurchase of convertible debt, reduction to additional paid-in capital	$ 107,900,000			(107,882,000)
Loss on extinguishment of debt			$ 7,800,000
Interest expense				13,000,000.0	15,300,000	14,600,000
Interest expense, excluding amortization				$ 1,500,000	$ 1,900,000	$ 1,900,000
Interest rate				0.625%	0.625%	0.625%
Amortization of convertible debt discount				$ 10,300,000	$ 12,000,000.0	$ 11,400,000
Amortization of debt issuance costs				1,200,000	1,400,000	$ 1,300,000
Long-term debt, fair value				243,800,000
Debt Issuance Costs, Net [Abstract]
Gross carrying amount				169,690,000	299,991,000
Unamortized debt discount				10,815,000	31,789,000
Debt issuance costs		$ 7,400,000		1,297,000	3,811,000
Net carrying amount				$ 157,578,000	$ 264,391,000
2022 Convertible Notes | Conversion option one
Debt Instrument [Line Items]
Threshold trading days | day		20
Threshold consecutive trading days | segment		30
Threshold percentage of stock price trigger		130.00%
2022 Convertible Notes | Conversion option two
Debt Instrument [Line Items]
Threshold trading days | day		5
Threshold percentage of stock price trigger		98.00%