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SENIOR CONVERTIBLE NOTES (Details) - USD ($)	3 Months Ended		6 Months Ended
SENIOR CONVERTIBLE NOTES (Details) - USD ($)	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Aug. 07, 2018
Debt Instrument [Line Items]
Unamortized discount						$ 8,200,000
Convertible senior notes payable	$ 94,637,000		$ 94,637,000		$ 93,514,000
Senior Notes \| Senior Unsecured Convertible Notes
Debt Instrument [Line Items]
Convertible debt, amount						$ 100,000,000.0
Debt interest rate						4.00%
Effective interest rate						6.00%
Unamortized discount	5,100,000		5,100,000		5,900,000
Unamortized debt issuance expense	2,000,000.0		2,000,000.0		2,300,000
Convertible debt, carrying amount of equity component	7,900,000		7,900,000
Accrued interest	1,700,000		1,700,000
Fair value of debt	79,100,000		79,100,000		$ 94,900,000
Recognized interest expense	$ 1,600,000	$ 1,600,000	$ 3,100,000	$ 3,100,000
Senior Notes \| Senior Unsecured Convertible Notes \| Pro Forma
Debt Instrument [Line Items]
Debt conversion price (in dollars per share)	$ 17.19		$ 17.19