Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following tables represent the fair value hierarchy for those assets and liabilities that the Company measures at fair value on a recurring basis (in thousands):

	Fair Value Measurements at December 31, 2017 Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	$	13,804	$	13,804	$	—	$	—
Short-term investments - commercial paper		14,982		—		14,982		—
Short-term investments - corporate notes		2,824		—		2,824		—
Short-term investments - corporate U.S. government    bonds		5,006		—		5,006		—
Investment		328		328		—		—
Total assets	$	36,944	$	14,132	$	22,812	$	—

	Fair Value Measurements at December 31, 2016 Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	$	6,522	$	6,522	$	—	$	—
Marketable securities - certificate of deposit		8,625		8,625		—		—
Investment		340		340		—		—
Total assets	$	15,487	$	15,487	$	—	$	—
Liabilities:
Derivative liability	$	8,795	$	—	$	—	$	8,795
Total liabilities	$	8,795	$	—	$	—	$	8,795

Summary of Changes in Fair Value of Company's Level 3 Financial Instruments

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial instruments (in thousands):

	Derivative Liability
Balance as of December 31, 2015	$	—
Issuance of convertible bonds with embedded derivative		8,262
Change in fair value		533
Balance as of December 31, 2016		8,795
Issuance of convertible bonds with embedded derivative		13,172
Change in fair value		15,411
Conversion of derivative liability to common stock		(37,378	)
Balance as of December 31, 2017	$	—