DEBT (Tables)

3 Months Ended

Mar. 31, 2019

Long-term Debt, Unclassified [Abstract]

Schedule of principal amount of the Senior Notes is repayable

The principal amount of the Senior Notes is repayable as of March 31, 2019 is as follows (amounts in thousands):

2019 (remainder)	$	95,000
2020	80,000
2021	82,500
Total	$	257,500

Summary of the carrying value of the Senior Notes

The following is a summary of the carrying value of the Senior Notes as of March 31, 2019 and December 31, 2018 (in thousands): 

	March 31, 2019			December 31, 2018
Principal amount of the Senior Notes	$	257,500		$	282,500
Unamortized debt discount balance	(2,077		)	(2,541		)
Unamortized debt issuance costs	(4,005		)	(1,650		)
Total Senior Notes	$	251,418		$	278,309

Summary of interest expense for the Notes

The following is a summary of interest expense for the three months ended March 31, 2019 and 2018 (in thousands):

	Three Months Ended March 31,
	2019		2018
Stated coupon interest	$	2,156	$	2,156
Amortization of debt discount and debt issuance costs	4,807		4,410
Total interest expense Convertible Notes	$	6,963	$	6,566

The following is a summary of interest expense for the three months ended March 31, 2019 and 2018 (in thousands): 

	Three Months Ended March 31,
	2019		2018
Contractual interest expense	$	8,206	$	10,441
Amortization of debt discount and debt issuance costs	1,357		1,008
Total interest expense Senior Notes	$	9,563	$	11,449

Summary of the liability component of the Convertible Notes

The following is a summary of the liability component of the Convertible Notes as of March 31, 2019 and December 31, 2018 (in thousands):

	March 31, 2019			December 31, 2018
Principal amount of the Convertible Notes	$	345,000		$	345,000
Unamortized discount of the liability component	(49,967		)	(54,521		)
Unamortized debt issuance costs	(2,429		)	(2,681		)
Total Convertible Notes	$	292,604		$	287,798