Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Financial Assets Measured at Fair Value on Recurring Basis

The following table summarizes the Company’s financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2018 and 2019 (in thousands):

	Carrying Amount as of December 31, 2018		Fair Value Measurements As of December 31, 2018
			Level 1		Level 2		Level 3
3.25% convertible senior notes due in 2020	$	27,974	$	—	$	—	$	27,974

	Carrying Amount as of December 31, 2019		Fair Value Measurements As of December 31, 2019
			Level 1		Level 2		Level 3
3.25% convertible senior notes due in 2020	$	—	$	—	$	—	$	—
3.25% convertible senior notes due in 2023	50,753		—		—		50,753
Preferred stock derivative liability	5,247		—		—		5,247

Reconciliation of Beginning and Ending Balances of Assets Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3)

The following table provides a reconciliation of the beginning and ending balances of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) (in thousands):

3.25% convertible senior notes due in 2020	Year ended December 31,
	2018			2019
Balance at January 1,	$	22,469		$	27,974
Issuance of 3.25% convertible senior notes	8,000			—
Additions	—			7,250
Loss on extinguishment of convertible senior notes	453			10,417
Extinguishment of convertible senior notes	—			(48,170		)
Change in fair value	(2,948		)	2,529
Balance at December 31,	$	27,974		$	—

3.25% convertible senior notes due 2023	Year ended December 31,
	2018		2019
Balance at January 1,	$	—	$	—
New issuance ($29.6 million face value)	—		37,916
New issuance ($8.0 million face value)	—		10,254
Change in fair value	—		2,583
Balance at December 31,	$	—	$	50,753

Preferred stock derivative liability	Year ended December 31,
	2018		2019
Balance at January 1,	$	—	$	—
New issuance of Series A Preferred Stock ($20.0 million face value)	—		4,894
Change in fair value	—		353
Balance at December 31,	$	—	$	5,247