Fair Value Measurements (Tables)

12 Months Ended

Dec. 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 consolidated balance sheets:

	As of December 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	$	9,145	$	—	$	—	$	468	$	—	$	—
Money market funds	52,996		—		—		44,481		—		—
Corporate bonds	—		6,339		—		—		9,262		—
Government securities - U.S.	—		12,701		—		—		19,050		—
Other fixed-income securities	—		9,409		—		—		4,250		—
Total assets	$	62,141	$	28,449	$	—	$	44,949	$	32,562	$	—
Related party payable (see Note 11)	—		—		28,840		—		—		98,925
Total liabilities	$	—	$	—	$	28,840	$	—	$	—	$	98,925