Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following table summarizes the financial instruments measured at fair value on a recurring basis classified in the fair value hierarchy (Level 1, 2 or 3) based on the inputs used for valuation in the accompanying condensed consolidated balance sheets:

	As of March 31, 2018						As of December 31, 2017
Fair Value Measurements:	Level 1		Level 2		Level 3		Level 1		Level 2		Level 3
Marketable securities (see Note 5)
Equity securities	$	10,163	$	—	$	—	$	468	$	—	$	—
Money market funds	60,059		—		—		44,481		—		—
Corporate bonds	—		41,314		—		—		9,262		—
Government securities - U.S.	—		36,777		—		—		19,050		—
Other fixed-income securities	—		8,956		—		—		4,250		—
Total assets	$	70,222	$	87,047	$	—	$	44,949	$	32,562	$	—
Related party payable (see Note 8)	—		—		72,767		—		—		98,925
Total liabilities	$	—	$	—	$	72,767	$	—	$	—	$	98,925