Debt (Tables)

6 Months Ended

Jun. 30, 2019

Debt Disclosure [Abstract]

Summary of Net Carrying Amount of Debt

The net carrying amounts of the liability components of the 2021 Notes as of June 30, 2019 and December 31, 2018 consists of the following (in thousands):

	June 30, 2019			December 31, 2018
Principal amount	$	300,000		$	300,000
Unamortized debt discount	(3,532		)	(4,348		)
Net carrying amount before unamortized debt issuance costs	296,468			295,652
Unamortized debt issuance costs	(5,430		)	(6,685		)
Net carrying value	$	291,038		$	288,967

Schedule of Interest Expense Recognized

The following table presents the interest expense recognized related to the 2021 Notes and 2018 Notes for the three and six months ended June 30, 2019 and 2018 (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Contractual interest expense at 1.5% and 5.75% per annum	$	4,313	$	5,261	$	8,625	$	10,522
Amortization of debt issuance costs	632		954		1,255		1,870
Accretion of debt discount	411		2,542		815		5,052
Total	$	5,356	$	8,757	$	10,695	$	17,444