DEBT (Details - Convertible Senior Notes) $ / shares in Units, $ in Thousands		6 Months Ended
	May 31, 2017 USD ($) day $ / shares Rate shares	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Aggregate principal amount of convertible senior notes	$ 300,000	$ 300,000		$ 300,000
Annual interest rate on convertible senior notes | Rate	0.625%
Initial conversion rate, shares per $1,000 principal amount of notes | shares	4.8163
Initial conversion price per share | $ / shares	$ 207.63
Conversion rate, sales price of common stock as a percentage of the conversion price | Rate	130.00%
Threshold trading days | day	5
Threshold consecutive trading days | day	5
Conversion rate, sales price of common stock as a percentage of the conversion price, five business days | Rate	98.00%
Cash repurchase at a price equal to the principal amount of the notes, Percentage | Rate	100.00%
Nonconvertible debt borrowing rate at the date of issuance | Rate	5.36%
Debt component of the principal amount of the Convertible Senior Notes	$ 238,400
Equity component of the principal amount of the Convertible Senior Notes	61,600
Financing costs related to the issuance of the Convertible Senior Notes	9,300
Debt issuance costs, liability component	7,400	4,541		5,252
Debt issuance costs, equity component	$ 1,900
Total interest expense on the Convertible Senior Notes		7,500	$ 7,200
Interest expense recognized associated with the 0.625% coupon rate		900	900
Amortization of convertible debt discount		5,929	5,623
Amortization of debt issuance costs		970	865
Long-term debt		257,582		250,943
Fair value of the Convertible Senior Notes using a Level 1 observable input		628,300
Unamortized debt discount		37,877		$ 43,805
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Amortization of debt issuance costs		$ 700	$ 700