LONG-TERM DEBT / INTEREST EXPENSE - Components of Convertible Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Liability component
Net carrying amount	$ 888,353	$ 1,152,322
Convertible Senior Notes \| Notes
Debt Instrument
Interest rate	1.50%
Liability component
Principal	$ 188,565	188,565
Conversion feature	(9,788)	(11,489)
Discount related to debt issuance costs	(1,337)	(1,572)
Net carrying amount	$ 177,440	$ 175,504

Convertible Debt, Liability Component [Abstract]

No definition available.

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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ 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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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

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