0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant

3 Months Ended

Mar. 31, 2018

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant

9. 0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant

In May 2017, the Company issued $350 million aggregate principal amount of 0.25% convertible senior notes due June 1, 2022 in a private offering and an additional $50 million aggregate principal amount of such notes pursuant to the exercise in full of the over-allotment options of the initial purchasers (the “2022 Notes”).

The net carrying amount of the liability component of the 2022 Notes is as follows:

	As of March 31, 2018			As of December 31, 2017
	(in thousands)
Principal	$	400,000		$	400,000
Unamortized debt discount		(89,931	)		(94,498	)
Unamortized issuance costs		(6,714	)		(7,055	)
Net carrying amount	$	303,355		$	298,447

Interest expense related to the 2022 Notes is as follows:

	Three Months Ended March 31,
	2018		2017
	(in thousands)
Contractual interest expense	$	250	$	—
Amortization of debt discount		4,567		—
Amortization of issuance costs		341		—
Total interest expense	$	5,158	$	—