Long-term Debt (Tables)

12 Months Ended

Dec. 31, 2018

Debt Instrument [Line Items]

Interest Expense Recognized Related to Convertible Notes

The following table sets forth the interest expense recognized related to the 2021 Notes (in thousands):

	Years Ended December 31,
	2018		2017		2016
Contractual interest expense	$	3,019	$	3,019	$	1,652
Amortization of debt discount		6,432		6,046		3,162
Amortization of debt issuance costs		943		833		416
Total interest expense related to the 2021 Notes	$	10,394	$	9,898	$	5,230

Debt, Liability Component [Member]

Debt Instrument [Line Items]

Net Carrying Amount of Convertible Debt

The net carrying amount of the liability component of the 2021 Notes was as follows (in thousands):

	December 31,
	2018			2017
Principal	$	172,500		$	172,500
Unamortized discount		(17,305	)		(23,737	)
Unamortized issuance cost		(2,801	)		(3,744	)
Net carrying amount	$	152,394		$	145,019

Debt, Equity Component [Member]

Debt Instrument [Line Items]

Net Carrying Amount of Convertible Debt

The net carrying amount of the equity component of the 2021 Notes was as follows (in thousands):

	December 31,
	2018			2017
Debt discount related to value of conversion option	$	32,945		$	32,945
Debt issuance cost		(1,179	)		(1,179	)
Net carrying amount	$	31,766		$	31,766