Convertible Senior Notes (Tables)

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Schedule of Debt

The 2022 Notes consist of the following:

Liability component	June 30, 2018			December 31, 2017
	(in thousands)
Principal	$	399,997		$	399,997
Less: Debt discount, net(1)	(55,899		)	(62,747		)
Net carrying amount	$	344,098		$	337,250

_______________________________________

⁽¹⁾  Included in the accompanying condensed consolidated balance sheets within convertible senior notes (due 2022) and amortized to interest expense over the remaining life of the 2022 Notes using the effective interest rate method.

The 2023 Notes consist of the following:

Liability component	June 30, 2018			December 31, 2017
	(in thousands)
Principal	$	402,500		$	402,500
Less: Debt discount, net(1)	(83,869		)	(90,552		)
Net carrying amount	$	318,631		$	311,948

_______________________________________

⁽¹⁾  Included in the accompanying condensed consolidated balance sheets within convertible senior notes (due 2023) and amortized to interest expense over the remaining life of the 2023 Notes using the effective interest rate method.

Schedule of Interest Expense

The following table sets forth total interest expense recognized related to the 2022 Notes:

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
	(in thousands)						(in thousands)
Contractual interest expense	$	2,500		$	2,500		$	5,000		$	5,000
Amortization of debt discount	3,434			3,205			6,848			6,392
Total	$	5,934		$	5,705		$	11,848		$	11,392
Effective interest rate of the liability component	6.5		%	6.5		%	6.5		%	6.5		%

The following table sets forth total interest expense recognized related to the 2017 Notes:

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
	(in thousands)						(in thousands)
Contractual interest expense	$	—		$	126		$	—		$	315
Amortization of debt discount	—			540			—			1,251
Total	$	—		$	666		$	—		$	1,566
Effective interest rate of the liability component	—		%	6.02		%	—		%	6.02		%

The following table sets forth total interest expense recognized related to the 2023 Notes:

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
	(in thousands)						(in thousands)
Contractual interest expense	$	2,767		$	2,767		$	5,534		$	5,526
Amortization of debt discount	3,351			3,104			6,682			6,179
Total	$	6,118		$	5,871		$	12,216		$	11,705
Effective interest rate of the liability component	7.5		%	7.5		%	7.5		%	7.5		%