Convertible Senior Notes (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Schedule of Debt

The 2023 Notes consist of the following:

Liability component	September 30, 2018			December 31, 2017
	(in thousands)
Principal	$	402,500		$	402,500
Less: Debt discount, net(1)	(80,408		)	(90,552		)
Net carrying amount	$	322,092		$	311,948

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⁽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.

The 2022 Notes consist of the following:

Liability component	September 30, 2018			December 31, 2017
	(in thousands)
Principal	$	399,997		$	399,997
Less: Debt discount, net(1)	(52,365		)	(62,747		)
Net carrying amount	$	347,632		$	337,250

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⁽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.

Schedule of Interest Expense

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

	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
	(in thousands)						(in thousands)
Contractual interest expense	$	2,500		$	2,500		$	7,500		$	7,500
Amortization of debt discount	3,535			3,298			10,383			9,690
Total	$	6,035		$	5,798		$	17,883		$	17,190
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 2023 Notes:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
	(in thousands)						(in thousands)
Contractual interest expense	$	2,768		$	2,767		$	8,302		$	8,293
Amortization of debt discount	3,461			3,205			10,143			9,384
Total	$	6,229		$	5,972		$	18,445		$	17,677
Effective interest rate of the liability component	7.5		%	7.5		%	7.5		%	7.5		%

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

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