DEBT (Tables)

6 Months Ended

Jun. 30, 2018

Senior Notes

Debt

Schedule of principal amount of the Senior Notes is repayable

The principal amount of the Senior Notes is repayable as of June 30, 2018 is as follows (amounts in thousands):

2018 (remainder)	$	25,000
2019		120,000
2020		80,000
2021		82,500
Total	$	307,500

Summary of the carrying value of the Senior Notes

The following is a summary of the carrying value of the Senior Notes as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30,		December 31,
	2018		2017
Principal amount of the Senior Notes	$	307,500	$	365,000
Unamortized debt discount balance		(3,589)		(4,717)
Unamortized debt issuance costs		(2,330)		(3,063)
Total Senior Notes	$	301,581	$	357,220

Summary of interest expense for the Notes

The following is a summary of interest expense for the three and six months ended June 30, 2018 and 2017 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Contractual interest expense	$	9,425	$	10,393	$	19,866	$	23,159
Amortization of debt discount and debt issuance costs		853		595		1,861		1,197
Total interest expense Senior Notes	$	10,278	$	10,988	$	21,727	$	24,356

Convertible debt

Debt

Summary of the liability component of the Convertible Notes

The following is a summary of the liability component of the Convertible Notes as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30,		December 31,
	2018		2017
Principal amount of the Convertible Notes	$	345,000	$	345,000
Unamortized discount of the liability component		(63,357)		(71,799)
Unamortized debt issuance costs		(3,186)		(3,691)
Total Convertible Notes	$	278,457	$	269,510

Summary of interest expense for the Notes

The following is a summary of interest expense for the three and six months ended June 30, 2018 and 2017 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Stated coupon interest	$	2,156	$	2,156	$	4,312	$	4,312
Amortization of debt discount and debt issuance costs		4,537		4,165		8,947		8,213
Total interest expense Convertible Notes	$	6,693	$	6,321	$	13,259	$	12,525