Convertible Senior Notes and Capped Calls (Tables)

6 Months Ended

Jun. 30, 2019

Debt Disclosure [Abstract]

Schedule of Liability and Equity Components of Convertible Debt

The net carrying amount of the liability component of the Notes was as follows:

	As of June 30, 2019			As of December 31, 2018
	(in thousands)
Principal	$	230,000		$	230,000
Unamortized debt discount	(45,690		)	(50,334		)
Unamortized issuance costs	(4,519		)	(4,978		)
Net carrying amount	$	179,791		$	174,688

The net carrying amount of the equity component as June 30, 2019 and December 31, 2018 was as follows (in thousands):

Debt discount for conversion option	$	53,820
Issuance costs	(1,626		)
Net carrying amount	$	52,194

Interest expense related to the Notes was as follows:

	Three Months Ended June 30, 2019		Six Months Ended June 30, 2019
	(in thousands)
Contractual interest expense	$	718	$	1,437
Amortization of debt discount	2,361		4,645
Amortization of issuance costs	233		459
Total interest expense	$	3,312	$	6,541

The net impact to our stockholders' equity, included in additional paid-in capital, of the above components of the Notes was as follows (in thousands):

Conversion option	$	53,820
Purchase of capped calls	(26,910		)
Issuance costs	(1,626		)
Total	$	25,284