Convertible Senior Debt (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Components of Notes

The Notes consist of the following (in thousands):

	September 30, 2018			December 31, 2017
Liability component:
Principal	$	143,750		$	—
Less: debt discount, net of amortization		(33,978	)		—
Net carrying amount	$	109,772			—
Equity component (a)		32,607			—

^(a) Recorded in the condensed consolidated balance sheet within additional paid-in capital, net of $1.1 million of issuance costs.

Interest Expense Recognized Related to Notes

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

	Nine Months Ended September 30,
	2018		2017
Contractual interest expense	$	657	$	—
Amortization of debt discount		3,029		—
Amortization of issuance costs		333		—
Total interest expense	$	4,019		—

Fair Value and Carrying Value of Convertible Senior Notes

As of September 30, 2018, the fair value of the Notes, which was determined based on inputs that are observable in the market or that could be derived from, or corroborated with, observable market data, quoted price of the Notes in an over-the-counter market (Level 2), and carrying value of debt instruments (carrying value excludes the equity component of the Company’s convertible notes classified in equity) were as follows (in thousands):

	September 30, 2018				December 31, 2017
	Fair Value		Carrying Value		Fair Value		Carrying value
Convertible senior notes	$	161,717	$	109,772		—		—