Convertible Senior Notes and Capped Calls (Tables)

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Schedule of Liability and Equity Components of Convertible Debt

The net carrying amount of the liability component of the 2023 Notes was as follows:

	As of March 31, 2020		As of December 31, 2019
	(in thousands)
Principal	$	230,000	$	230,000
Unamortized debt discount	(38,271)		(40,768)
Unamortized issuance costs	(3,785)		(4,032)
Net carrying amount	$	187,944	$	185,200

The net carrying amount of the equity component as March 31, 2020 and December 31, 2019 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 2023 Notes was as follows:

	Three Months Ended March 31,
	2020		2019
	(in thousands)
Contractual interest expense	$	719	$	719
Amortization of debt discount	2,496		2,284
Amortization of issuance costs	247		226
Total interest expense	$	3,462	$	3,229

The net impact to our stockholders' equity, included in additional paid-in capital, of the above components of the 2023 Notes was as follows (in thousands):

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