DEBT (Convertible Senior Notes) (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	May 31, 2017 USD ($) day $ / shares Rate shares	Dec. 31, 2019 USD ($) Rate	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Aggregate principal amount	$ 300,000	$ 299,991	$ 300,000
Interest rate | 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 | Rate	130.00%
Threshold trading days | day	5
Threshold percentage of stock price trigger | Rate	98.00%
Redemption percentage | Rate	100.00%
Nonconvertible debt borrowing rate at the date of issuance | Rate	5.36%
Convertible debt, noncurrent	$ 238,400
Carrying amount of debt, equity component	61,600
Debt issuance costs, gross	9,300
Debt issuance costs, equity component	1,900
Interest expense		$ 15,300	14,600	$ 8,200
Interest expense, excluding amortization		1,900		1,100
Amortization of convertible debt discount		12,016	11,397	6,385
Amortization of debt issuance costs		1,974	1,776	1,032
Long-term debt, fair value		469,100
Debt Issuance Costs, Net [Abstract]
Gross carrying amount	300,000	299,991	300,000
Unamortized debt discount		31,789	43,805
Debt issuance costs	$ 7,400	3,811	5,252
Net carrying amount		264,391	250,943
Convertible Debt
Debt Instrument [Line Items]
Interest expense, excluding amortization			1,900
Amortization of convertible debt discount			11,400
Amortization of debt issuance costs		$ 1,400	$ 1,300	$ 700