Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Summary of the Levels of the Fair Value Hierarchy into Which the Company's Financial Assets Fall

The following table summarizes the levels of the fair value hierarchy into which the Company’s financial assets fall as of September 30, 2018:

	Total		Level 1			Level 2			Level 3
Financial assets:
Included in cash and cash equivalents
Government securities money market	$	34,521	$	—		$		34,521	$	—
Investments
Government debt securities (1)		1,817			—			1,817			—
U.S. treasury instruments		142,877			45,301			97,576		—
Common stock		243			243		—				—
Total financial assets	$	179,458	$		45,544	$		133,914	$		—

(1) Consists of municipal bonds and agency bonds.

The following table summarizes the levels of the fair value hierarchy into which the Company’s financial assets fall as of December 31, 2017:

	Total		Level 1			Level 2			Level 3
Financial assets:
Included in cash and cash equivalents
Government debt securities (1)	$	41,086	$		—	$		41,086	$	—
U.S. treasury instruments		39,978		—				39,978		—
Government securities money market		46,095		—				46,095		—
Investments
Government debt securities (1)		39,910			—			39,910		—
U.S. treasury instruments		55,935			7,943			47,992			—
Common stock		263			263		—			—
Total financial assets	$	223,267	$		8,206	$		215,061	$		—

(1) Consists of municipal bonds, agency bonds and agency discount notes