DEBT (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Summary of the carrying values

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

	December 31,
	2019			2018
Principal amount of the Senior Notes	$	162,500		$	282,500
Unamortized debt discount balance	(4,035		)	(2,541		)
Unamortized debt issuance costs	(2,022		)	(1,650		)
Total Senior Notes	$	156,443		$	278,309

Summary of interest expense

The debt discount and debt issuance costs are amortized as interest expense using the effective interest method. The following is a summary of interest expense for the 2024 Notes for year ended December 31, 2019 (in thousands):

	December 31,
	2019
Stated coupon interest	$	2,250
Amortization of debt discount and debt issuance costs	2,583
Total interest expense 2024 Notes	$	4,833

The debt discount and debt issuance costs are amortized as interest expense using the effective interest method. The following is a summary of Senior Notes interest expense for 2019, 2018 and 2017 (in thousands):

	December 31,
	2019		2018		2017
Contractual interest expense	$	25,559	$	38,242	$	44,212
Amortization of debt discount and debt issuance costs	5,783		3,589		2,631
Total interest expense	$	31,342	$	41,831	$	46,843

The debt discount and debt issuance costs are amortized as interest expense using the effective interest method. The following is a summary of interest expense for 2019, 2018 and 2017 (in thousands):

	December 31,
	2019		2018		2017
Stated coupon interest	$	6,708	$	8,624	$	8,625
Amortization of debt discount and debt issuance costs	15,398		18,288		16,784
Total interest expense 2021 Notes	$	22,106	$	26,912	$	25,409

Summary of the liability components

The 2024 Notes are not convertible or redeemable as of December 31, 2019. The following is a summary of the liability component of the 2024 Notes as of December 31, 2019 (in thousands):

	December 31,
	2019
Principal amount of the 2024 Notes	$	120,000
Unamortized discount of the liability component	(51,701		)
Unamortized debt issuance costs	(2,796		)
Total 2024 Notes	$	65,503

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

	December 31,
	2019			2018
Principal amount of the 2021 Notes	$	145,000		$	345,000
Unamortized discount of the liability component	(14,963		)	(54,521		)
Unamortized debt issuance costs	(725		)	(2,681		)
Total 2021 Notes	$	129,312		$	287,798