CONVERTIBLE NOTES (Tables)

3 Months Ended

Mar. 31, 2020

CONVERTIBLE NOTES.

Schedule of Convertible note obligations included in the condensed consolidated balance sheets

(In thousands)	Coupon Interest Rate	Effective Interest Rate	Fair Value of Liability Component at Issuance (1)		March 31, 2020		December 31, 2019
2028 Convertible notes	0.375%	5.2%	$	790,608	$	1,150,000	$	—
2027 Convertible notes	0.375%	6.3%	472,501		747,500		747,500
2025 Convertible notes	1.000%	6.0%	227,103		315,049		415,049
Total Convertible notes	​	​			2,212,549		1,162,549
Less: Debt discount (2)	​	​			(667,228)		(342,463)
Less: Debt issuance costs (3)	​	​			(31,015)		(16,481)
Net convertible debt	​	​			$	1,514,306	$	803,605

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(1)As each of the convertible instruments may be settled in cash upon conversion, for accounting purposes, they were separated into a liability component and an equity component. The amount allocated to the equity component is the difference between the principal value of the instrument and the fair value of the liability component at issuance. The resulting debt discount is being amortized to interest expense at the respective effective interest rate over the contractual term of the debt. A portion of the 2025 Convertible Notes have been extinguished or converted. The fair value of the liability component at issuance reflected above represents the liability value at issuance for the applicable portion of the 2025 Notes which remain outstanding at March 31, 2020 and December 31, 2019. The fair value of the liability component of the 2025 Notes at issuance was $654.8 million with the equity component being $269.7 million.

(2)The unamortized discount consists of the following:​

(In thousands)	March 31, 2020		December 31, 2019
2028 Convertible notes	$	356,145	$	—
2027 Convertible notes	246,362		253,340
2025 Convertible notes	64,721		89,123
Total unamortized discount	$	667,228	$	342,463

(3)Debt issuance costs consists of the following:​

(In thousands)	March 31, 2020		December 31, 2019
2028 Convertible notes	$	16,621	$	—
2027 Convertible notes	9,899		10,251
2025 Convertible notes	4,495		6,230
Total debt issuance costs	$	31,015	$	16,481

Schedule of Allocation of Transaction Costs Related to Convertible Debt

The following table summarizes the original transaction costs at the time of issuance for each set of Notes and the respective allocation to the liability and equity components:

(In thousands)	January 2025 Notes		June 2025 Notes		2027 Notes		2028 Notes
Transaction costs allocated to:
Liability component	$	13,569	$	5,052	$	11,395	$	16,811
Equity component	5,340		2,311		6,632		7,642
Total transaction costs	$	18,909	$	7,363	$	18,027	$	24,453

Schedule of interest expense

Interest expense includes the following:​

	Three Months Ended March 31,
(In thousands)	2020		2019
Debt issuance costs amortization	$	822	$	685
Debt discount amortization	13,731		8,394
Loss on settlement of convertible notes	7,954		10,558
Coupon interest expense	1,932		2,108
Total interest expense on convertible notes	24,439		21,745
Other interest expense	714		245
Total interest expense	$	25,153	$	21,990