DEBT / INTEREST EXPENSE - Components of Convertible Debt (Details) - Convertible Senior Notes - Notes - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Instrument
Interest rate	1.50%
Liability component
Principal	$ 159,097		$ 159,097
Conversion feature	(2,356)	$ (3,900)	(3,898)
Discount related to debt issuance costs	(314)		(524)
Net carrying amount	$ 156,427	$ 156,400	$ 154,675

Convertible Debt, Liability Component [Abstract]

No definition available.

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- Definition

Amount of short-term and long-term debt and lease obligation.

+ References

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- Definition

Amount of a favorable spread to a debt holder between the amount of debt being converted and the value of the securities received upon conversion. This is an embedded conversion feature of convertible debt issued that is in-the-money at the commitment date.

+ References

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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount, after accumulated amortization, of debt discount.

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